Field of the Invention

The present invention concerns improvements in or relating to security documents. More particularly, but not exclusively, this invention concerns a method of authenticating a security document having a plurality of inclusions (e.g. fibres or planchettes) having one or more afterglow (e.g. phosphorescent) regions, inclusions, security document and security devices for use in such a method, methods of manufacture of such inclusions and security documents, and portable electronic devices and computer program products for use in such a method.

Background of the Invention

Security documents, for example banknotes, passports, lottery tickets, tax stamps, some certificates and other items of potentially high value, are targets for counterfeiters, who seek to produce counterfeit copies of the security documents and thus illegally benefit from the high value of the genuine items. Security documents typically include various security features (devices) that are difficult for a counterfeiter to simulate.

In order to be effective, a security feature must exhibit characteristics that are easily identified by a user seeking to verify the authenticity of the security document concerned whilst increasing the burden for a potential counterfeiter. To that end, many security documents include fluorescent security features. Typically, the fluorescent materials used in security documents emit visible light when illumined with ultraviolet light. However, the need for an ultraviolet light source may limit the use, particularly by private individuals, of such security features to verify a security document. Accordingly, it would be advantageous to provide methods of verifying security documents that are more widely applicable.

WO 2004/025028 (D W Spinks (Embossing) Ltd) discloses a fluorescent security feature, namely a fibre for inclusion into a security document having a plurality of differently coloured regions printed on front and rear sides, wherein the colours are visible only under ultra-violet light. Such security fibres take the form of small strips of paper, for example approximately 4 mm x 0.3 mm, that can be added to the paper pulp during manufacture. The provision of a plurality of fibres in a paper product can result in an overall pattern that is unpredictable and difficult to replicate, yet relatively straightforward to describe.

It is also known to use phosphorescence as a security feature in a security document. In comparison to fluorescence which stops emitting light almost as soon as illumination stops, phosphorescent materials release the radiation they have absorbed relatively slowly and can be energised using visible light. Depending on the materials used this can be over a period of seconds, minutes or hours although most phosphorescent materials still emit over a periods in the order of milliseconds. For the avoidance of doubt, phosphorescence and fluorescence are both types of photoluminescence but are different and distinct phenomena resulting from different transitions between energy states. In particular, phosphorescence involves an intersystem crossing into an energy state of different spin multiplicity (that is a change in electron spin). Phosphorescence is also typically characterized by a bigger Stokes shift than fluorescence.

Typically, phosphorescent materials emit light at much lower intensities than fluorescent materials and, in practice, phosphorescence of the type used in security documents is typically only visible in low-light conditions (for example at illuminance levels of less than 100 lux). Accordingly, such phosphorescent materials are of limited use in verifying a security document in everyday use. Recent developments in phosphorescent security features have tended to focus on relatively complex features, see for example EP 1 316 924 (AGFA- GEVAERT) which relates to the use of storage phosphors that are energised and then emit light upon exposure to light having a wavelength longer than the emission wavelength of the phosphor itself. Again, the complexity of such features may limit the circumstances in which they can be used to verify a document.

The present invention seeks to mitigate the above-mentioned problems.

The burden on counterfeiters is also increased when legitimate producers of security documents have a variety of security devices and effects from which to choose. Consequently, it is advantageous to provide new security devices and methods of verification per se.

A security document may include public or open features designed to allow a broad range of users to verify the document and private or covert features that require specialist knowledge or equipment to validate. The inclusion of different layers of security features further increases the burden on counterfeiters. Consequently, it is advantageous to provide security devices and methods of verification that provide both public and private features.

Alternatively or additionally, the present invention seeks to provide an improved security devices for security documents and/or methods of verification of security documents.

Summary of the Invention

In a broadest aspect of the present disclosure there is provided a method of authenticating a security document The security document may comprise at least one afterglow region, for example at least one phosphorescent region. The method may comprise one or more of the following steps:

- illuminating the security document with a flash of visible light,

- at a first predetermined time after the flash, capturing a first image of the security document; and - authenticating the security document in dependence on the appearance of the security document in the first image

In a first aspect of the invention, there is provided a method of authenticating a security document, the security document comprising a document substrate and a plurality of inclusions incorporated into the document substrate. Each inclusion comprises: a substrate (an inclusion substrate) and at least one phosphorescent region on a first and/or second side of the substrate, the phosphorescent region emitting visible light. Each inclusion may comprise at least one coloured region on a first and/or second side of the substrate, the coloured region reflecting light when viewed under visible light, and at least part of said at least one phosphorescent region does not overlap with any coloured region on the same side of the substrate (the inclusion substrate). Additionally or alternatively, each inclusion comprises at least one fluorescent region on a first and/or second side of the substrate, the fluorescent region being substantially invisible when viewed under visible light and emitting light when viewed under ultraviolet light, and at least part of said at least one phosphorescent region does not overlap with any fluorescent region on the same side of the substrate (the inclusion substrate). The method comprises:

- illuminating the security document with a flash of visible light;

- at a first predetermined time after the flash, capturing a first image of the security document; and

- authenticating the security document in dependence on the appearance of the security document in the first image.

Thus, methods in accordance with the present invention may involve energizing the afterglow regions, for example phosphorescent regions, of a security document using a flash and then capturing an image of the document at a predetermined time after the flash. The appearance of an afterglow region, for example phosphorescent region, will change over time in a predictable manner as the emission intensity of the region decays following energisation. The appearance of the security document, and more particularly the afterglow or phosphorescent regions, in the first image may therefore by used to verify the authenticity of the security document. For example, if the regions are visible in the first image this may provide an indication to the user that the document is authentic. Conversely, if the regions are not visible in the first image this may provide an indication to the user that the document is not authentic.

Methods in accordance with the present invention use an inclusion having (i) a coloured region that is visible under visible light (e.g. daylight) and/or a fluorescent region that is visible under ultraviolet light, and (ii) a phosphorescent region, at least part of which does not overlap with any coloured region and/or fluorescent region. The presence of the coloured and/or fluorescent region may allow a user to easily detect the location of an inclusion in the security document substrate, authentication can then be carried out by analysing and/or capturing an image of only that region of the document in which the inclusion is present. This may allow the image to be captured at a shorter distance from the document, making the phosphorescent emission easier to detect with a camera and/or facilitate authentication by removing the need to consider the whole surface area of the document. Having a portion of the phosphorescent region that does not overlap with the coloured or fluorescent region allows this to take place without reducing the intensity of the phosphorescent response - the intensity being reduced if, for example, the coloured region and/or fluorescent region is printed over or under the phosphorescent region. A coloured region may be particularly advantageous in allowing the location of the inclusion in a document substrate without the need for specialist equipment such as UV lights.

Illuminating the security document with a flash and capturing an image thereafter may allow the method to be carried out under relatively high levels of ambient lighting thereby increasing the ease of use of the method and/or the range of circumstances in which the method may usefully be employed because the flash energizes the phosphorescent region to a higher level than, for example, ambient visible light, and the image can be captured very shortly thereafter while the phosphorescent regions are still emitting relatively high levels of light. It may be that the method is carried out in daylight. For example, it may be that the method can be carried out at an illuminance of more than 200 lux, for example more than 1000 lux, for example more than 10,000 lux.

Additionally or alternatively, it may be that following energization with the flash the afterglow regions only emit light at a detectable level for a short period of time (for example in the order of milliseconds) and consequently without capturing the image there is insufficient time for a user to analyse the appearance of the document in order to validate the document. Capturing the image may therefore enable validation of a security document using a rapidly-decaying (and therefore difficult to counterfeit) visual effect.

Additionally or alternatively, capturing the image may facilitate automation of the validation process, for example by allowing a computer program to analyse the captured image and provide an indication to a user as to the validity of the document.

Additionally or alternatively, methods in accordance with the present invention may increase the burden on counterfeiters.

An afterglow region may be defined as a region that emits (rather than reflects) visible light following the end of illumination. The or each afterglow region may be a phosphorescent region. A phosphorescent region may be defined as a region that emits visible light as a result of phosphorescence. Such a region may be provided using phosphorescent materials, for example phosphorescent inks. The phosphorescent region may be provided by printing, for example screen printing, phosphorescent inks onto a surface of the inclusion. The phosphorescent region may emit light in a first colour.

A coloured region may be defined as a region that reflects (rather than emits) visible light. Such a region may be providing using coloured inks. The coloured region may be provided by printing, for example screen printing, coloured inks onto a surface of the inclusion. The coloured region may reflect light of a second, different, colour, or reflect light of the first colour, under visible light.

A fluorescent region may be defined as a region that emits visible light as a result of fluorescence, for example when viewed under ultraviolet (UV) light. The fluorescent region may be (substantially) invisible under visible light but appear coloured when viewed under UV light. The fluorescent region may emit light of the first colour, the second colour, or a third, different, colour when viewed under UV light. Such a region may be provided using fluorescent materials, for example fluorescent inks. The fluorescent region may be provided by printing, for example screen printing, fluorescent inks onto a surface of the inclusion. It may be that the fluorescent region is substantially free from phosphorescent materials. The fluorescent region may emit light of the first colour, the second colour, or a third, different, colour. An inclusion may comprise a plurality of fluorescent regions, each region emitting light of a different colour under ultraviolet light.

It may be that each inclusion comprises at least one coloured region on a first and/or second side of the substrate and at least one fluorescent region on a first and/or second side of the substrate. It may be that said at least part of said at least one phosphorescent region does not overlap with any coloured region on the same side of the substrate and/or does not overlap with any fluorescent region on the same side of the substrate.

The inclusion may comprise a substrate having a first and second surface. The first surface may be on a first side of the inclusion (or substrate). The second surface may be on a second, opposite, side of the inclusion (or substrate). The thickness of the substrate may be very much less than the surface area of the first or second surface of the substrate. It may be that the substrate is sheet-like. The substrate may be a paper or cellulose-based substrate, or a polymer substrate.

At least one phosphorescent region may be printed on the first and/or second surface of the substrate At least one coloured region may be printed on the first and/or second surface of the substrate. At least one fluorescent region may be printed on the first and/or second surface of the substrate. The inclusion may be printed on both its first and second sides by printing on one of the sides and allowing the ink to soak or bleed through to the other side of the inclusion. Alternatively, the inclusion may be printed on both its first and second sides by printing on one side of the inclusion and then printing on the other side of the inclusion. Where a phosphorescent region is printed on the first and second side, the requirement that “at least part of said at least one phosphorescent region does not overlap with any coloured region or any fluorescent region on the same side of the substrate” may be understood as requiring that there is no overlap on at least one of the first and second sides.

Said at least part of a phosphorescent region that does not overlap with any coloured region and/or any fluorescent region on the same side of the substrate may cover at least 20 percent, for example at least 30%, for example at least 40% of the surface area of said side of the substrate. Thus, there may be a substantial surface region of the inclusion where the phosphorescent region does not overlap with any coloured or fluorescent region.

It may be that said at least part of a phosphorescent region that does not overlap with any coloured region and/or any fluorescent region on the same side of the substrate also does not overlap with any coloured region and/or any fluorescent region on the other side of the substrate to the phosphorescent region. Said at least part of a phosphorescent region that does not overlap with any coloured region and/or fluorescent region on the same or a different side of the substrate may cover at least 20 percent, for example at least 30%, for example at least 40% of the surface area of said side of the substrate.

It may be that said at least part of a phosphorescent region that does not overlap with any coloured region and/or any fluorescent region on the same side of the substrate is on an otherwise unprinted (i.e. free from print) region of the surface of the inclusion on that side. Providing a phosphorescent region on a surface where no other printing takes place may limit any reduction in intensity of light emitted by the phosphorescent materials.

It may be that no part of the phosphorescent region overlaps with any colour region either (i) on the same side of the substrate or (ii) on both the same side and a different side of the substrate. That is to say, the phosphorescent region and any colour region(s) may be non overlapping.

It may be that no part of the phosphorescent region overlaps with any fluorescent region either (i) on the same side of the substrate or (ii) on both the same side and a different side of the substrate. That is to say, the phosphorescent region and any fluorescent region(s) may be non overlapping.

It may be that at least one coloured region and at least one phosphorescent region are arranged such that in an overlap region light emitted from the phosphorescent region passes through the coloured region to produce a third, different, colour. Such an overlap region may provide a striking visual effect and further increase the burden on the counterfeiter. The step of authenticating the security document may include authenticating the document in dependence on whether the overlap region is visible in the first image. It may be that at least one fluorescent region and at least one phosphorescent region are arranged such that in an overlap region light emitted from the phosphorescent region mixes with light emitted by the fluorescent region under UV light to produce a third, different, colour. Such an overlap region may provide a striking visual effect and further increase the burden on the counterfeiter. The step of authenticating the security document may include authenticating the document in dependence on whether the overlap region is visible in an image captured under UV illumination.

The coloured region and/or fluorescent region may be on the same side of the substrate and/or the other side of the substrate as the phosphorescent region in the overlap region. The inclusion may be arranged such that the overlap region appears the third, different, colour (e.g. a different colour to the phosphorescent region and the coloured region and/or fluorescent region in question) when viewed in the first image and/or following illumination with the flash. If the coloured region and/or fluorescent region is on the other side of the substrate to the phosphorescent region, it may be that the substrate is substantially transparent or transparent to visible light, for example such that light emitted by the phosphorescent region can be perceived by a user and/or captured on an image (e.g. the first image or a subsequent image) after passing through the substrate and the coloured region and/or fluorescent region.

It may be that at least one phosphorescent region and at least one coloured region are printed on the same one of the first and second surfaces, at least part of the coloured region being printed over only part of the phosphorescent region to produce an overlap region.

It may be that at least one phosphorescent region and at least one coloured region are printed on different ones of the first and second surfaces to produce an overlap region.

It may be that at least one phosphorescent region and at least one fluorescent region are printed on the same one of the first and second surfaces, at least part of the fluorescent region being printed over only part of the phosphorescent region to produce an overlap region.

It may be that at least one phosphorescent region and at least one fluorescent region are printed on different ones of the first and second surfaces to produce an overlap region.

It may be that an afterglow region (e g. a phosphorescent region) is energized by the flash of visible light. It may be that, following energisation, a region emits visible light at an intensity that varies with respect to time. Each region may have an emission decay profile which describes the variation in emission intensity of visible light from that region with respect to time following energization. The emission decay profile of a region may comprise a peak where the emission intensity of that region reaches a maximum followed by a period of decay during which the emission intensity reduces. It will be appreciated that for a given level of energization, afterglow regions (e.g. phosphorescent regions) of different types, for example produced using different (phosphorescent) materials, may have different emission decay profiles. For example different peak emission intensities when exposed to the same flash of visible light and/or different profdes in terms of the rate and/or shape of the profde in the period of decay.

It may be that before the security document is illuminated with the flash of visible light the afterglow (e.g. phosphorescent) region is not visible, for example the region emits substantially no visible light. The first predetermined time may be a time at which the emission intensity of the region is such that the region is visible in the first image. The method may comprise authenticating the security document in dependence on whether the region is visible in the first image. For example, the method may comprise determining that the security document is genuine if the at least one region is visible in the first image. Likewise, the method may comprise determining that the security document is not genuine if the at least one region is not visible in the first image.

At one level, the step of authenticating the document may simply involve determining whether the inclusions and/or afterglow regions are present in the document (i.e. whether any such regions are visible in the document). At another level, the step of authenticating the document may comprise determining whether the afterglow regions on an inclusion are correctly arranged in accordance with the predetermined appearance. Thus, methods in accordance with the present invention may allow for different levels of security, for example for use by different types of users, in verifying the document.

The method may further comprise the step of: at an initial time, capturing an initial image of the security document; and authenticating the security document in dependence of the appearance of the security document in the initial image and the first image.

The initial time may be before or after the first predetermined time. In the case that the inclusion comprises at least one coloured region, the first predetermined time may be a time before the flash. The method may comprise authenticating the security document in dependence on whether the coloured region is visible in the initial image and/or the phosphorescent region is not visible in the first image. The method may comprise authenticating the document in dependence on the difference between the initial and first images. Thus, the method may comprise determining the document is authentic if: (i) the coloured region but not the phosphorescent region is visible in the initial image and (ii) the phosphorescent region is visible in the first image.

In the case the inclusion comprises at least on fluorescent region, the method may comprises capturing an initial image under ultraviolet light and authenticating the security document in dependence on the presence of the fluorescent regions in the initial image and the presence of the phosphorescent regions in the first image.

The method may comprise a user identifying the location of at least one inclusion in the security document substrate using the coloured regions and/or the fluorescent regions; and then capturing the first image (or any other image as described below). The method may comprise the user positioning the camera so as to capture the first image (or any other image as described below) of only a part of the security document which includes said at least one inclusion. Said part of the security document may be only a part of the security document that is visible to the user at the time the image is captured. Thus, the method may comprise taking only a partial image of the security document which targets the inclusion and authenticating the document in dependence on said partial image. This may allow the image to be captured at a shorter distance from the document then would otherwise be the case, making the phosphorescent emission easier to detect with a camera and/or facilitate authentication by removing the need to consider the whole surface area of the document.

It may be the phosphorescent region further comprises fluorescent materials in addition to the phosphorescent materials. It may be that under ultraviolet (UV) light, said fluorescent materials emit visible light of the same colour or a different colour as that emitted by the phosphorescent region. It may be that said fluorescent materials are (substantially) invisible under visible light. Such a region may be provided by printing, for example screen printing, inks comprising both phosphorescent and fluorescent materials. Inks comprising both phosphorescent and fluorescent materials may be provided by mixing both fluorescent and phosphorescent pigments into the ink. For example, it may be that at least 50% by weight of the pigment in the ink is fluorescent pigment and/or between 50% and 20% by weight of the pigment in the ink is phosphorescent pigment. Alternatively, inks comprising both phosphorescent and fluorescent materials may be provided by mixing fluorescent and phosphorescent inks. For example, an ink may comprise at least 50% (by volume) fluorescent ink and/or between 50% and 20% (by volume) phosphorescent ink. Said fluorescent materials may be substantially invisible when viewed under visible light such that phosphorescent regions including the fluorescent materials are substantially invisible under visible light prior to illumination with the flash.

The method may further comprise the step of illuminating the document with UV light and authenticating the document in dependence on the appearance of the document under UV light and in the first image. For example, the method may comprise determining the document is authentic if the phosphorescent regions appear the same colour or a different colour under UV light and in the first image. Inclusion of fluorescent materials emitting light of the same of different colour as the phosphorescent materials in this manner may provide a striking visual effect and/or further increase the burden on a counterfeiter.

It may be that the security document, e.g. the inclusion, comprises at least one afterglow (e.g. phosphorescent) region of a first type and at least one afterglow (e.g. phosphorescent) region of a second type, the afterglow region of the first type having a first emission decay profile and the afterglow region of the second type having a second emission decay profile, the method further comprising the step of:

- at a second predetermined time after the flash, capturing a second image of the security document; and

- authenticating the security document in dependence on the appearance of the security document in the first and second images.

Thus, methods in accordance with the present invention may use afterglow regions, for example phosphorescent regions, having differing emission decay profiles to provide visually striking and difficult to reproduce effects. Methods in accordance with the present invention may be used to provide a wide range of such effects by using several different types of afterglow (e.g. phosphorescent) regions and a series of images. They may also provide for different levels of security features in the same document. For example capture of a single image or first set of images for a public-level security feature and a second, different, set of images for a private-level security feature. Additionally or alternatively capturing a series of images may enable authentication of a security document using a rapidly-decaying (and therefore difficult to counterfeit) visual effect. Additionally or alternatively, use of afterglow regions with different emission decay profiles and a series of images may allow for a large number of permutations in terms of the appearance to be achieved thereby increasing the burden on the counterfeiter.

In the case that inclusion comprises an overlap region, the appearance of the overlap region, for example the colour the overlap region appears, may change over time as the emission of the phosphorescent region decays. This may produce a visually striking and difficult to reproduce effect. The method further comprise the step of:

- at a second predetermined time after the flash, capturing a second image of the security document; and

- authenticating the security document in dependence on the appearance of the security document in the first and second images, for example in dependence on the change in appearance of the overlap region between the first and second image.

It may be that the where the inclusion comprises at least one afterglow (e.g. phosphorescent) region of a first type and at least one afterglow (e.g. phosphorescent) region of a second type, the coloured region and the afterglow regions of the first and second types are arranged such that in the overlap region, light emitted from the phosphorescent regions of the first and second types passes through the coloured region to produce a colour that is different from that emitted by each of the each of the phosphorescent regions and reflected by the coloured region. This may further enhance the colour shifting effect in the overlap regions.

The second predetermined time may be later than the first predetermined time. The first predetermined time may be a time at which the emission intensity of the afterglow regions of the first and second types is such that the afterglow regions of the first and second types are visible in the first image. The second predetermined time may be a time at which the emission intensity of the afterglow regions of the first and/or second types is reduced, for example by more than 10 percent, for example by more than 50 percent, in comparison to the emission intensity at the first predetermined time. The second predetermined time may be a time at which the emission intensity of the afterglow regions of the first and second types is such that the afterglow regions of one of the first and second type are visible in the second image, and the afterglow regions of the other one of the first and second type are not visible in the second image.

The step of authenticating the security document in dependence on the appearance of the security document in the first and second images may comprise authenticating the security document in dependence on the difference in appearance of the afterglow (e.g. phosphorescent) regions of the first and/or second type between the first image and the second image. It may be that the afterglow regions of both the first and second type are visible in the first image, the afterglow regions of one of the first and second type are visible in the second image, and the afterglow regions of the other one of the first and second type are not visible in the second image. Additionally or alternatively, the method may comprise authenticating the security document in dependence on a change in the brightness of the afterglow regions of the first and/or second type as between the first and second images.

The security document may comprise afterglow (e.g. phosphorescent) regions of a third, fourth and/or further types. Each different type of region may have a different emission decay profile from any other type of region. For example, the afterglow region of the third type may have a third emission decay profile, the fourth type may have a fourth emission decay profile and any further types (if present) may have further emission decay profile(s).

An inclusion may comprise a plurality of afterglow (e.g. phosphorescent) regions, each region emitting light of a different colour and having a different emission decay profile. Each afterglow region (e.g. phosphorescent region) may comprise fluorescent materials that fluoresce in the same colour or a different colour under UV light as the phosphorescent materials in that region. The method may comprise capturing a third image of the security document at a third predetermined time after the flash, a fourth image of the security document at a fourth predetermined time after the flash and/or further image(s) of the security document at further predetermined time(s) after the flash. The third predetermined time may be later than the second predetermined time. The third predetermined time may be a time at which the emission intensity of the afterglow regions of one or more of the first, second, and third types is reduced, for example by more than 10 percent, for example by more than 50 percent, in comparison to the emission intensity at the second predetermined time . The fourth predetermined time may be later than the third predetermined time. The fourth predetermined time may be a time at which the emission intensity of the afterglow regions of one or more of the first, second, third and fourth types is reduced, for example by more than 10 percent, for example by more than 50 percent, in comparison to the emission intensity at the third predetermined time. Any further predetermined time(s) may be later than the fourth predetermined time.

The step of authenticating the security document may comprise authenticating the security document in dependence on the appearance of the afterglow (e.g. phosphorescent) regions in the first, second, third, fourth and/or further images, for example by comparing the appearance with the expected appearance of said regions. The method may comprise authenticating the security document in dependence on the difference in appearance of the afterglow (e.g. phosphorescent) regions between the first, second, third and fourth images.

It may be that in the first image a first set of afterglow (e.g. phosphorescent) regions are visible. It may be that in the second image a second set of afterglow (e.g. phosphorescent) regions are visible. It may be that in the third image a third set of afterglow (e.g. phosphorescent) regions are visible. It may be that in the fourth image a fourth set of afterglow (e.g. phosphorescent) regions are visible. It may be that in any further image(s) further set(s) of afterglow (e.g. phosphorescent) regions are visible. Each set of afterglow (e.g. phosphorescent) regions may comprise a different combination of types of afterglow regions (e.g. different types of phosphorescent regions) to any other set.

It may be that at the first predetermined time, the emission intensity of the afterglow regions of the first, second (if present), third (if present), fourth (if present), and further (if present) types is such that the phosphorescent regions of the first, second (if present), third (if present), fourth (if present), and further (if present) types are visible in the first image.

It may be that the emission intensity of the afterglow regions of the second type declines between the first and second predetermined times such that said regions are not visible in the second (or any subsequent) image. It may be that at the second predetermined time, the emission intensity of the afterglow regions of the first, third (if present), fourth (if present), and further (if present) types is such that the afterglow regions of said types are visible in the second image.

It may be that the emission intensity of the afterglow regions of the third type declines between the second and third predetermined times such that said regions are not visible in the third (or any subsequent) image. It may be that at the third predetermined time, the emission intensity of the afterglow regions of the first, fourth (if present), and further (if present) types is such that the phosphorescent regions of said types are visible in the third image.

It may be that the emission intensity of the afterglow regions of the fourth type declines between the third and fourth predetermined times such that said regions are not visible in the fourth (or any subsequent) image. It may be that at the fourth predetermined time, the emission intensity of the afterglow regions of the first, and further (if present) types is such that the phosphorescent regions of said types are visible in the fourth image.

It may be that the emission intensity of the afterglow regions of the first type declines between the fourth and a final predetermined time such that said regions are not visible in a final image captured at the final predetermined time after the flash.

The method may comprise authenticating the security document in dependence on one or more of (i) whether and/or which afterglow (e.g. phosphorescent) regions are visible in a given image (e.g. the first, second, third or fourth image), (ii) whether and/or how the appearance of the afterglow (e.g. phosphorescent) regions is different as between images (e.g. the first and second, second and third and/or third and fourth images), (iii) comparing the appearance of the afterglow regions in the captured images with the appearance in a corresponding series of reference images (e.g. first, second, third and/or fourth reference images). The step of authenticating the security document may comprise determining that the security document is genuine in dependence on one or more of (i) the correct afterglow regions being visible in a given image, (ii) the correct change in appearance taken place between different images, (iii) the appearance matching that of the reference images. Likewise, the method may comprise determining that the security document is not genuine if one or more those criteria is not met.

It may be that the security document is not illuminated with a flash of visible light between the capturing of: the first and second images, the second and third images and/or the third and fourth images.

It may be that afterglow (e.g. phosphorescent) regions of the first type emit visible light of a first colour. It may be that afterglow (e.g. phosphorescent) regions of the second type emit visible light of a second, different, colour. It may be that afterglow (e.g. phosphorescent) regions of the third, fourth and further (if present) types emit visible light of a third, fourth and further, different, colours respectively

It may be that the security document (e.g. the inclusion) comprises one or more coloured regions that reflect (as opposed to emit) visible light to appear coloured when viewed under visible light. The security document may comprise first coloured regions that appear a first colour when viewed under visible light. The security document may comprise second coloured regions that appear a second, different, colour when viewed under visible light. The security document may comprise third and fourth coloured regions that appear a third and fourth colours when viewed under visible light. The coloured regions may overlap with the afterglow (e.g. phosphorescent) regions. For example, the first coloured regions may overlap with afterglow regions of the first type, the second coloured regions may overlap with afterglow regions of the second type and so on. The coloured regions may be used to indicate the presence of the afterglow regions (particularly where inclusions are used, see below) to a user. Similarly, the security document (or inclusion) may comprise first fluorescent regions that appear a first colour when viewed under ultraviolet light. The security document may comprise second fluorescent regions that appear a second, different, colour when viewed under ultraviolet light and so on.

It may be that the afterglow (e.g. phosphorescent) regions individually and/or together appear as a symbol, geometric shape (e.g. circle, square, rectangle, diamond, star) or image when viewed while emitting light.

It may be that the afterglow (e.g. phosphorescent) regions are arranged in a repeating pattern. Said regions may be stripes, forming a repeating pattern of stripes. It may be that adjacent stripes emit light of different colours when energized. It may be that each stripe is immediately adjacent to another stripe. Alternatively, it may be that the repeating pattern of stripes comprises a repeating pattern of spaces between stripes.

It may be that afterglow (e.g. phosphorescent) regions of different types (e.g. the first, second, third (if present), fourth (if present) and/or further (if present) types) overlap, for example fully or partially. In the case that the afterglow (e.g. phosphorescent) regions of the first and second types overlap it may be that the colour of a region of the security document changes as between the first and second image (for example as result of the emissivity of the region of the second type reducing more rapidly than the emissivity of the region of the first type). Likewise, where third, fourth or further types of afterglow regions are present these may overlap with the phosphorescent regions of the first and second types thereby providing colour changes between the second and third images and/or third and fourth images depending on the number of different types of regions present. For example, it may be that afterglow regions of the first, second and third types overlap thereby providing a change in colour between the first and second images and the second and third images as the emission intensity of the different types of regions decays at different rates.

It may be that afterglow (e.g. phosphorescent) regions of different types do not overlap. It may be that phosphorescent regions of different types are arranged contiguously in a repeating pattern.

It may be that the coloured regions are arranged in a repeating pattern. Said regions may be stripes, forming a repeating pattern of stripes. It may be that adjacent stripes reflect light of different colours when viewed under visible light. It may be that each stripe is immediately adjacent to another stripe. Alternatively, it may be that the repeating pattern of stripes comprises a repeating pattern of spaces between stripes.

It may be that the fluorescent regions are arranged in a repeating pattern. Said regions may be stripes, forming a repeating pattern of stripes. It may be that adjacent stripes emit light of different colours when viewed under UV light. It may be that each stripe is immediately adjacent to another stripe. Alternatively, it may be that the repeating pattern of stripes comprises a repeating pattern of spaces between stripes.

It may be that the coloured regions and/or fluorescent regions and phosphorescent regions are arranged in a repeating pattern. Said regions may be stripes, forming a repeating pattern of stripes. It may be that adjacent stripes reflect or emit light of different colours. It may be that each stripe is immediately adjacent to another stripe. Alternatively, it may be that the repeating pattern of stripes comprises a repeating pattern of spaces between stripes. It may that two or more stripes overlap to produce an overlap region, for example a repeating pattern of overlap regions.

It may be that the or each phosphorescent region extends over the entire width of the inclusion. It may be that the or each phosphorescent region extends over a continuous area occupying at least 10%, for example at least 20%, for example at least 40%, for example at least 50% of the surface area of one side of the inclusion.

It may be that the or each coloured region and/or the or each fluorescent region extends over the entire width of the inclusion. It may be that the or each coloured region and/or the or each fluorescent region extends over a continuous area occupying at least 10%, for example at least 20%, for example at least 40%, for example at least 0% of the surface area of one side of the inclusion.

It may be that the or each part of the phosphorescent region that does not overlap with any coloured region and/or any fluorescent region extends over the entire width of the inclusion. It may be that the or each part of the phosphorescent region that does not overlap with a coloured region and/or any fluorescent region extends over a continuous area occupying at least 10%, for example at least 20%, for example at least 40%, for example at least 50% of the surface area of one side of the inclusion.

The step of authenticating the security document may comprise a user looking at the or each image (e.g. the first, second, third, fourth image), for example to see if the afterglow (e.g. phosphorescent) regions and/or overlap regions are present and/or have the expected appearance. The step of authenticating the security document may comprise a user looking at the initial image, for example to see if the coloured regions are present and/or have the expected appearance.

The step of authenticating the security document may comprise a computer analysing the or each image (e.g. the first, second, third, fourth image), for example using image recognition to identify the afterglow (e.g. phosphorescent) regions and/or overlap regions visible in an image and/or the type of afterglow (e.g. phosphorescent) regions visible in an image. It may be that in dependence on whether the afterglow (e.g. phosphorescent regions) and/or overlap regions are present in the or each image and/or have the expected appearance, the computer provides an indication to the user as to the authenticity of the security document. The step of authenticating the security document may comprise a computer analysing the initial image, for example using image recognition to identify the coloured regions. It may be that in dependence on whether the coloured regions are present in the or each image and/or have the expected appearance, the computer provides an indication to the user as to the authenticity of the security document

The step of authenticating the security document may comprise a user looking at the document and the computer providing an indication as to the authenticity of the security document. Thus methods in accordance with the present invention may increase the reliability of authentication by assisting a user in reaching a determination as to authenticity.

Alternatively, it may be that the step of authenticating the security document in is carried out wholly by the computer. That is to say, it may be that the user relies on the indication from the computer, for example without looking at the image themselves. Thus, methods in accordance with the present invention may increase the ease and/or reliability of authentication - for example by removing the need for a user to remember what the appearance of the phosphorescent regions should be in a particular document. This may be particularly advantageous for complicated and/or precise visible effects.

It may be that the arrangement of afterglow (e.g. phosphorescent regions), for example the location of different types of regions, in a document is unique to that document. For example the regions may be included on a plurality of inclusions (see below) in a security-document substrate forming part of the security document. In that case, the method may comprise authenticating the security document in dependence on whether the appearance of the security document matches the appearance of the security document in a previously captured image of the security document. Thus, methods in accordance with the present invention may use a previously captured image of the security document to subsequently authenticate the security document, for example based on the random distribution of the inclusions in a security-document substrate used in the production of the security document. That is to say, the random distribution of the inclusions in the security-document substrate may be used as a unique identifier (or code) for that document thereby increasing the burden on any counterfeiter.

The term “a previously captured image of the security document” may refer to an image of the security document that is to be authenticated (e.g. the security document itself and not, for example, another security document which can serve as a reference/example as in the case of security features that are reproduced across many documents). The previously captured image may have been captured days, weeks months, or years previously, for example by the issuing authority. The step of authenticating the security document may be carried out by the issuing authority and/or an end user. The previously captured image may be captured at or before the time the security document is issued by the issuing authority.

The method may comprise comparing the first, second, third and/or fourth images (if present) with first, second, third and/or fourth previously captured images of the documents. It may be that each previously-captured image was taken at a predetermined time after a flash of visible light (being a different flash of visible light from that on which the timing of the taking of the first, second, third and/or fourth images is based) corresponding to a predetermined time of the method (e.g. the first, second, third and/or fourth predetermined time). Thus, the first image is compared with a first previously-captured image captured at the first predetermined time, the second image with a second previously-captured image captured at the second predetermined time and so on.

Authenticating the security document in dependence on whether the appearance of the afterglow (e.g. phosphorescent) regions matches that of a previously captured image of the security document may comprise analysing the appearance of individual afterglow regions and, optionally, comparing the colour and/or location of said afterglow regions in one or more images with the colour and/or location of said phosphorescent regions in one or more previously-captured images. Authenticating the security document in dependence on whether the appearance of the afterglow regions matches that of a previously captured image of the security document may comprise analysing the appearance of individual inclusions and, optionally, comparing the colour and/or location of said inclusions in one or more images with the colour and/or location of said inclusions in one or more previously-captured images. Additionally or alternatively, in dependence on whether the appearance of the afterglow regions matches that of a previously captured image of the security document may comprise analysing the appearance of individual afterglow regions on a security thread and, optionally, comparing the colour and/or location of said afterglow regions in one or more images with the colour and/or location of said afterglow regions in one or more previously-captured images.

The previously captured image(s) may be stored in a database, for example by the issuing authority. The method may comprise accessing the database, for example on a remote server, to obtain a copy of the previously captured image. The step of accessing the database may be carried out by a portable electronic device in response to a user command and/or as part of an automated process to provide an indication as to the authenticity of the security document to a user.

The method may comprise using image recognition software to compare the appearance of the security devices in the image(s) and the previously captured image(s).

The method may comprise using a flash unit to illuminate one or more of said phosphorescent regions with a flash of visible light. The flash unit may be configured to produce a flash of artificial visible light. The flash unit may be built into a camera, or the portable electronic device. The flash unit may be a standalone flash unit.

The method may comprise using a camera, for example a digital camera, to capture the first, second, third and/or fourth images. The camera may be a standalone camera or a camera built into a portable electronic device.

The method may comprise capturing the or each image of the security document in the absence of ambient light, for example while the security document is in the dark. For example, the camera or portable electronic device comprising the camera may be arranged with respect to the security document such that substantially all ambient light is excluded (for example by the body of the camera or portable electronic device or a separate shield). For example, it may be that the method can be carried out at an illuminance of less than 50 lux, for example less than 5 lux, for example less than 0.002 lux, for example less than 0.0001 lux. The camera or portable electronic device may be positioned in close proximity to, for example placed on, the security document such that substantially all ambient light is excluded. This may increase the visibility of the afterglow regions, allow a wider range of materials to be used and/or for more subtle changes in appearance to be detected thereby increasing the burden on counterfeiters.

The security document may comprise a security document substrate. The phosphorescent regions may comprise afterglow (e.g. phosphorescent) regions on a first and/or second, opposite, surface of an inclusion (see below) incorporated into the security document substrate. The afterglow (e.g. phosphorescent) regions may comprise regions on a first and/or second, opposite, surface of a security thread (see below) incorporated into a security document substrate. Additionally or alternatively the regions may be printed on a first and/or second, opposite, surface of the security document substrate. Additionally or alternatively the regions may be printed on a transfer, for example a sticker or label affixed to the security document substrate. Thus, methods in accordance with the present invention may be used with a variety of security features including those provided by printing onto the security document substrate, by incorporating inclusions into the security document substrate, by incorporating security thread(s) into the security document substrate and/or by applying or affixing a transfer to the security document substrate.

The afterglow regions may comprise printed regions. The afterglow regions may be phosphorescent regions, said phosphorescent regions may comprise printed phosphorescent regions, for example screen-printed phosphorescent regions. Phosphorescent inks are commercially available from manufacturers such as Petrel, Sun-Luminescent, Mirage Ink, and Sicpa and any appropriate ink may be used. For example, the Series 320-PEQxx, 320- PHQxx, 388-PEQxx, 388-PHQxx, 640-PEQxx and 640-PHQxx inks are phosphorescent inks available from Printcolor Screen Ltd of Berikon, Switzerland.

As used herein the term ‘visible’ may be understood as requiring that the afterglow (e.g. phosphorescent) region is detectable in the image. It may be that there is a threshold level of emission intensity below which a afterglow region is not visible. This will vary depending on a number of factors, including for example the level of ambient light, the equipment used to capture the image, the way in which the region is detected (e.g. by eye or automatic image analysis) and/or any post processing used. It will be appreciated that the method is carried out under a given set of conditions (e.g. ambient light and/or equipment) that remain substantially constant for the duration of the method such that it is time elapsed since the flash that is the main factor in determining whether a region of a given type is visible in an image. It may be that (for the conditions under which the method is carried out) a region of a given type is not visible (e.g. detectable) in a captured image before illumination with the flash but is visible (e.g. detectable) for a period thereafter. Similarly, it will be appreciated that when considering methods in which a series of images of a security document having regions of different types is used the method requires a change in the appearance of those regions across the series of images. That change may be that a region of a given type is visible (e g. detectable) in one or more images in that series but not visible (e.g. not detectable) in others. Additionally or alternatively, it may be that the appearance of a region changes between different images in the series. For example, that a region of one type appears brighter in one image than another or that the colour of said regions changes as between different images. It will be appreciated that any visible light of an appropriate wavelength (for example daylight) will, to some extent, energize the regions but that the light emitted as a result of such energization is essentially negligible in comparison to the levels of light emitted following energization by a flash (which may provide a significantly more intense level of illumination). The afterglow regions may be substantially invisible prior to illumination with the flash when viewed under visible light.

The flash may have a duration during which the flash illuminates the security document and any phosphorescent region(s) therein. The duration may be defined as the length of time the light intensity of a flash is above 0.1 (10%) of the peak intensity. The flash of visible light may have a duration between 0.5 and 10 milliseconds, for example between 1 and 5 milliseconds. The end of the flash may be defined as the time at which the light intensity falls below 90%, of the peak intensity of the flash. Each predetermined time may be measured from the end of the flash used to illuminate the document.

In some embodiments the first predetermined time may be less than 1 second, for example less than 0.5 seconds, for example less than 0.05 seconds after the end of the flash. The time between each of the first and second, second and third (if present) and/or third and fourth (if present) predetermined times may be less than 1 second, for example less than 0.5 seconds, for example less than 0.05 seconds.

In other embodiments, the first predetermined time may be more than 1 second, for example more than 1.5 seconds, for example more than 5 seconds after the end of the flash and (optionally) less than 10 seconds after the end of the flash. The time between each of the first and second, second and third (if present) and/or third and fourth (if present) predetermined times may be more than 1 second, for example more than 1.5 seconds, for example more than 5 seconds and (optionally) less than 10 seconds after the end of the flash.

The coloured regions may comprise printed regions, for example screen-printed coloured regions.

The security document may comprise a machine-readable image, for example a QR code. The machine readable image may be configured to provide a prompt to a user to download a computer program product configured to cause a portable electronic device to execute one or more steps in accordance with the method and/or to provide a link to a remote server where a computer program product (or software product) configured to execute one or more steps of the method is available. Additionally and/or alternatively, the machine- readable image may provide a link to a database, for example on a remote server, where the previously-captured image(s) are available and/or a link to the previously-captured image(s) in the database. The security document may comprise a reference code, for example an alphanumeric reference code visible under visible light, that allows the user to locate the previously captured image(s) in a database of such images.

The security document may comprise one or more indicia, visible in visible light. The indicia may indicate the presence of the afterglow (e.g. phosphorescent) regions.

One or more of the steps of the method described above may be carried out using a personal electronic device. The personal electronic device may be a smart phone, tablet or other similar device. The computer may be a personal electronic device. Using a personal electronic device in the method may increase the ease with which a security document can be verified. Additionally or alternatively, using a personal electronic device in the method may increase the range of circumstances in which the method can usefully be employed, particularly by private individuals.

The method may comprise using the personal electronic device to produce the flash of visible light and/or to capture the image(s). It may be that the image(s) captured is/are displayed on a screen of the portable electronic device. It may be that the computer program runs on a processor(s) of the portable electronic device. It may be that the screen and/or speaker of the portable electronic device are used to provide a visual and/or audible indication as to the authenticity of the document.

The portable electronic device may carry out one or more of the steps of the method of authenticating the security document (for example illuminating the security document, capturing one or more images, authenticating the security document, obtaining one or more previously-captured images, comparing the captured one or more images and the one or more previously captured images, and/or providing an indication of the authenticity of the document), for example in response to a user input, for example a user input to initiate the authentication process. It may be that following that initiation the steps are carried out automatically (e.g. without further user input). Thus, the portable electronic device may be configured to take the first, second, third and/or fourth images at the corresponding predetermined time without user intervention. In this way, use of a portable electronic device may increase the accuracy of the method and/or enable taking of images at intervals in the order of milliseconds.

The portable electronic device may compare one or more images (e.g. the first, second image and so on) of the security document and one or more previously-captured images of the security document and provide an indication to a user as to the authenticity of the document in dependence on the afterglow (e.g. phosphorescent) regions in the image and the previously-captured image. Such a comparison may be carried out using conventional image recognition software. There may be a number of inclusions in the security-document substrate such that it would be difficult and/or time consuming for a user to accurately compare the appearance of the inclusions with a previously captured image using the naked eye. Thus, use of a portable electronic device may increase the usability of the method of authenticating the document. For example there may be more than twenty, for example more than fifty, for example more than one hundred inclusions in a security document.

In an aspect of the invention there is provided a security document substrate having a plurality of inclusions as described above or below incorporated therein. It may be that each inclusion has a first surface and a second surface opposite the first surface, the first and/or second surface comprising one or more afterglow (e.g. phosphorescent) regions.

In an aspect of the invention there is provided a security document comprising such a security document substrate. Such a security document may be verified using the method and apparatus described above. Additionally or alternatively, the incorporation of inclusions having afterglow (e.g. phosphorescent) regions into the substrate of the security document may provide a striking visual effect and/or a visual effect that is difficult for counterfeiters to reproduce. The security document may have any of the features of the security document as described above in connection with the method of the invention. The security document substrate may be a paper or cellulose-based substrate, or a polymer substrate.

It may be that the plurality of inclusions comprises a first set of inclusions and a second set of inclusions, each inclusion of the first set having an afterglow (e.g. phosphorescent) region of a first type on a first and/or second surface and each inclusion of the second set having an afterglow (e.g. phosphorescent) region of a second type on a first and/or second surface. As discussed above, it may be that the afterglow regions of the first type having a first emission decay profile and the afterglow regions of the second type having a second, different, emission decay profile. It may be that each inclusion of the first set has a coloured region on a first and/or second surface and each inclusion of the second set has a coloured region of a different colour on a first and/or second surface. Similarly, the plurality of inclusion may comprise third and fourth sets of inclusions, the inclusions of said sets having afterglow regions of the third and fourth types respectively and differently coloured coloured regions.

An inclusion may be defined as a device that is incorporated into the pulp used to produce the security document substrate, for example the paper, from which a security document is produced. Inclusions may be incorporated into the pulp by mixing the inclusions with slurry paper pulp and forming the paper pulp and inclusion mix into a continuous web of paper. Each inclusion may be a planchette, a fibre, a starlight. Each inclusion may have a first surface and a second, opposite surface. One or both of the first and second sides may have one or more afterglow (e.g. phosphorescent) regions printed on said side(s).

In an aspect of the invention, there is provided an inclusion for incorporation into the substrate of a security document, the inclusion comprising: a substrate and at least one phosphorescent region on a first and/or second side of the substrate, the phosphorescent region emitting visible light. The inclusion may comprise at least one coloured region on a first and/or second side of the substrate, the coloured region reflecting light of a second, different, colour when viewed under visible light; and wherein at least part of said at least one phosphorescent region does not overlap with any coloured region on the same side of the substrate. Additionally or alternatively, the inclusion may comprise at least one fluorescent region on a first and/or second side of the substrate, the fluorescent region being substantially invisible when viewed under visible light and emitting light when viewed under ultraviolet light, and at least part of said at least one phosphorescent region does not overlap with any fluorescent region on the same side of the substrate.

Each inclusion may have any of the features described above or below with reference to the method of the invention or any other aspect of the invention. Each inclusion may be venfied using the method of the invention as described above or below.

The one or more afterglow (e.g. phosphorescent) regions may cover the majority, for example the whole, of the first and/or second surface of the inclusion. It may be that a single phosphorescent region covers the majority, for example the whole, of the first and/or second surface of the inclusion.

The one or more coloured regions may cover the majority of the first and/or second surface of the inclusion. It may be that a single coloured region covers the majority of the first and/or second surface of the inclusion.

The one or more fluorescent regions may cover the majority of the first and/or second surface of the inclusion. It may be that a fluorescent region covers the majority of the first and/or second surface of the inclusion.

It may be that the inclusion comprises a first margin. It may be that the inclusion comprises a second margin. It may be that the or each margin is an unprinted region (i.e. a region free from print) being an unprinted region on at least one surface of the inclusion, for example an unprinted region on both surfaces of the inclusion.

The provision of such a margin may provide greater adhesion when the inclusion is embedded in the security document substrate that an inclusion without such a margin. Additionally or alternatively, such a margin may provide a margin of error when producing the inclusion. The inclusion may be cut from a substrate, for example a sheet of paper, such that the cutting takes place in the margin(s). A certain level of inaccuracy during the cutting process can thus be tolerated, as it no longer affects the appearance of the printed region, which will still appear to be in perfect register. This may be of particular importance where each inclusion includes both a coloured region and a phosphorescent region, as the omission or reduction in the area of either could impact significantly on the visual appearance of the inclusion.

The inclusion may comprise a printed region made up of (i) at least one coloured region and/or at least one fluorescent region, and (ii) at least one phosphorescent region. The or each margin may be adjacent to the printed region, for example adjacent a coloured region, fluorescent region or a phosphorescent region. A margin may be adjacent said at least part of said at least one phosphorescent region that does not overlap with any coloured region and/or fluorescent region on the same side of the substrate. The printed region may comprise a plurality of coloured regions, a plurality of fluorescent regions and/or a plurality of phosphorescent regions, for example as a plurality of stripes arranged in a repeating pattern.

The appearance of the substrate of the inclusion may match the appearance of the security document substrate under visible light. Thus, it may be (depending on the appearance of the coloured and/or fluorescent regions) that the inclusion is substantially invisible in the substrate in visible light.

Each inclusion may comprise a first margin, the first margin being adjacent to the printed region and extending between the printed region and a first edge of the inclusion. Each inclusion may comprise a second margin, the second margin being adjacent to the printed region and extending between the printed region and a second, different, edge of the inclusion such that the printed region is located between the first and second margins. The printed region may be located approximately at the centre of the fibre, with the first margin and second margin located at respective ends of the fibre. In the case the inclusion is a planchette, a first margin may extend around a portion of the perimeter, for example the majority of the perimeter, for example the whole of the perimeter of the planchette. The coloured region and/or fluorescent region may be located approximately at the centre of the planchette with the margin extending around the edges of the planchette.

Fibres are discussed in WO 2004/025028, entitled “Rainbow Fibres” filed in the name of D W Spinks (Embossing) Ltd, the contents of which are incorporated herein by reference. A fibre may be a strip of paper suitable for incorporation into the substrate of a security document (a security substrate). Each fibre may have a length of between 3 mm and 10 mm and/or a width of the between 0. 125 mm and 0.5 mm. Each fibre may comprise a fibre substrate having a first surface and a second, opposite, surface. The fibre substrate may be transparent. The fibre substrate may be paper. The fibre substrate may be tissue paper or alternative thin paper. The fibre substrate may be with or without optical brighteners. The fibre substrate may be paper of a high porosity, high wet strength tissue paper with a nominal basis weight of between 23 and 28 g/m2. The fibre substrate may be paper of a high porosity, high wet strength tissue paper with a nominal basis weight of 25 g/m2.

Planchettes are discussed in WO 2007/144657, entitled “Planchette for use in counterfeit protection” filed in the name of D W Spinks (Embossing) Ltd, the contents of which are incorporated herein by reference. Each planchette may be a planar element suitable for incorporation into the substrate of a security document (a security document substrate). A planchette may be circular in shape, such that each planchette has the form of a disc. Alternatively other shapes of planchette may be used, for example the shape of the planchette may be that of a symbol, regular shape (triangle, square, rectangle, diamond, star), and/or irregular shape. Each planchette may have a maximum dimension of between 6 mm and 2 mm.

A starlight may be defined as a micro-cut particle for inclusion in a security document substrate. The maximum dimension of the starlight may be between 100pm and 2000 pm, for example between 200pm and 1000 pm.

In another aspect of the invention there is provided a method of authenticating a security document comprising a security document substrate having at least one printed region on a first and/or second side of the substrate, the printed region having a geometric shape, each printed region comprising a phosphorescent region on a first and/or second side of the substrate, the phosphorescent region emitting visible light and

(i) at least one coloured region on a first and/or second side of the substrate, the coloured region reflecting light when viewed under visible light, and within said printed region at least part of said at least one phosphorescent region does not overlap with any coloured region on the same side of the security-document substrate and/or

(ii) at least one fluorescent region on a first and/or second side of the security document substrate, the fluorescent region being substantially invisible when viewed under visible light and emitting light when viewed under ultraviolet light, and within said printed region at least part of said at least one phosphorescent region does not overlap with any fluorescent region on the same side of the security document substrate, and the phosphorescent region and coloured region and/or fluorescent region together define the geometric shape of the printed region; the method comprises:

- illuminating the security document with a flash of visible light;

- at a first predetermined time after the flash, capturing a first image of the security document; and - authenticating the security document in dependence on the appearance of the security document in the first image. There may also be provided a security document substrate suitable for use in such a method.

Thus, the security document substrate may have a continuous printed region (e.g. a region without unprinted regions therein) defined by at least one phosphorescent region and one or both of at least one coloured region and at least one fluorescent region. The printed region may form a geometric shape printed on a surface of the security-document substrate, for example a circle, rectangle, triangle, square, star or other shape. Thus, it may be that in at least part of the printed region the phosphorescent region does not overlap with a coloured region and/or a fluorescent region on the same side of the substrate. The printed region may have any of the features described with reference to inclusion, in which context references to the substrate may be understood as applying equally to the security document substrate when considering the printed region (except when clearly incompatible). A security document having a security document substrate may be authenticated using any of the methods described above or below. The phosphorescent, fluorescent and/or coloured regions in a printed region may be on the same side of the security document substrate. The printed region may include an overlap region in which the phosphorescent region overlaps with the fluorescent and/or coloured regions as described above.

In an aspect of the invention, there is provided a security document comprising a substrate. The substrate may have a security thread incorporated therein and/or a security stripe affixed thereto. The security thread or stripe may have a first surface and a second surface opposite the first surface, the first and/or second surface comprising one or more afterglow (e.g. phosphorescent) regions.

The security thread may be wholly or partially embedded within the substrate. It may be that the security thread is a windowed security thread, for example with a plurality of portions of the thread embedded within the substrate, said portions being interspersed with portions of the thread that are partially embedded within the substrate so as to form a surface of the substrate.

The thread may be a metallised polyester. The thread may have regions that are demetallized so that these regions are transparent. The thread may be holographic, for example with partially de-metallised regions. The polyester thread may have printed areas that are opaque to transmitted light Additionally or alternatively, the thread may comprise printed and unprinted regions so that some of said regions are transparent to transmitted light.

To apply the thread to the security document, it may be that a foil or laminate thread with afterglow (e.g. phosphorescent) regions is applied to the surface of the substrate or document. It may be that the foil is applied using a hot stamping or rolling process, it may be that the laminate is applied with hot melt or cold set wet adhesive, it may be that the foil or laminate is applied using a uv curable adhesive.

The security stripe may be affixed to the substrate, for example by an adhesive layer. The stripe may comprise a substrate (or carrier) having a width of between 10 and 20 mm. The substrate may be polyester, or a cast material, for example a uv cast material and (optionally) be provided on a transfer layer before being affixed to the document.

Such a security document may be verified using the method and apparatus described above. Additionally or alternatively, the incorporation of a security thread having afterglow (e.g. phosphorescent) regions into the substrate of the security document may provide a striking visual effect and/or a visual effect that is difficult for counterfeiters to reproduce. The security document may have any of the features of the security document as described above in connection with the method of the invention.

It may be that the first and/or second surface of the security thread comprises one or more afterglow (e.g. phosphorescent) regions of a first type and one or more afterglow (e.g. phosphorescent) regions of a second type, the regions of the first type having a having a first emission decay profile and the regions of the second type having a second, different, emission decay profile. Similarly, the first and/or second surface of the security thread may comprise regions of the third and fourth types. The security thread may comprise any of the features e g. phosphorescent regions, coloured regions and/or fluorescent regions as described with respect to the inclusions.

In an aspect of the invention, there is provided an inclusion (or set of inclusions) for incorporation into a substrate of a security document. The or each inclusion(s) may comprise a first surface and a second surface opposite the first surface, the first and/or second surface comprising one or more afterglow (e.g. phosphorescent) regions. It may be that the first and/or second surface comprises one or more afterglow regions of a first type and one or more afterglow regions of a second type, the afterglow regions of the first type having a having a first emission decay profile and the afterglow regions of the second type having a second, different, emission decay profile. The inclusion(s) may have any of the features of the security thread as described above.

In an aspect of the invention, there is provided a security thread for incorporation into a substrate of a security document. The security thread comprises a first surface and a second surface opposite the first surface, the first and/or second surface comprising one or more afterglow (e.g. phosphorescent) regions. It may be that the first and/or second surface comprises one or more regions of a first type and one or more regions of a second type, the regions of the first type having a having a first emission decay profile and the regions of the second type having a second, different, emission decay profile. The security thread may have any of the features of the security thread as described above.

In an aspect of the invention there is provided a method of manufacturing an inclusion for incorporation into a security-document substrate, the method comprising the steps of: printing a plurality of phosphorescent regions on a first and/or second surface of a substrate in the form of a sheet, the phosphorescent regions emitting visible light; printing a plurality of coloured regions on a first and/or second surface of the substrate, the coloured regions reflecting light when viewed under visible light and/or printing a plurality of fluorescent regions on a first and/or second surface of the substrate, the fluorescent regions being substantially invisible when viewed under visible light and emitting light when viewed under ultraviolet light; and cutting the substrate to create an inclusion including at least one of the phosphorescent regions and

(i) at least one of the coloured regions and wherein at least part of said at least one phosphorescent region does not overlap with any coloured region on the same side of the substrate and/or

(ii) at least one of the fluorescent regions wherein at least part of said at least one phosphorescent region does not overlap with any fluorescent region on the same side of the substrate.

The method may comprise said plurality of phosphorescent regions and coloured regions are arranged in a plurality of printed regions, each printed region being bounded at least in part by a margin, the margin being an unprinted region of at least one surface of the substrate, the substrate being cut in the margins.

The method may be used to produce inclusions having any of the features described above in connection with the inclusions of the invention.

In an aspect of the invention there is provided a method of manufacturing a securitydocument substrate mixing one or more of the inclusions of the invention as described above, or one or more inclusions manufactured using the method described above, with slurry paper pulp such that the inclusions form a hydrogen bond with the cellulose fibre in the paper pulp; and forming the paper pulp and inclusion mix into a continuous web of paper.

In further aspects of the invention there is provided a portable electronic device adapted to execute one or more steps of the method of authenticating a security document and a computer program product comprising instructions to cause a portable electronic device to execute one or more steps of the method of authenticating a security document.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

Figure 1 shows a schematic view of a portion of a security document according to a first embodiment of the invention at (a) a first time, (b) a second time, (c); a third time and (d) a fourth time/prior to illumination with a flash.

Figure 2 shows a schematic plot of emission intensity vs time for the phosphorescent regions of the first embodiment;

Figure 3 shows a flow chart of an example method of authenticating a security document in accordance with the invention;

Figure 4 shows a schematic plot of emission intensity vs time for the phosphorescent regions of a second example embodiment

Figure 5 shows a schematic view of a bank note in accordance with a third example embodiment of the invention (a) prior to illumination, (b) at a first time after illumination and (c) in a first image displayed on a smart phone;

Figure 6 shows a schematic view of a fibre in accordance with a fourth example embodiment of the invention;

Figure 7 shows a schematic view of a bank note including a plurality of fibres in accordance with the fourth embodiment (a) prior to illumination and (b) at a first time after illumination;

Figure 8 shows an example method of manufacturing the bank note of the fourth embodiment;

Figure 9 shows a schematic view of a security fibre according to a fifth example embodiment of the invention at (a) a first time, (b) a second time, (c); a third time, (d) a fourth time and (e) a fifth time/prior to illumination with a flash

Figure 10 shows a schematic view of a portion of a security document including a plurality of fibres in accordance with the fourth embodiment.

Figure 11 shows a schematic view of a planchette in accordance with a sixth example embodiment of the invention; Figure 12 shows a schematic view of a portion of a security thread according to a seventh embodiment of the invention at (a) a first time, (b) a second time, (c); a third time and (d) a fourth time;

Figure 13 shows a schematic view of a security document including a security thread in accordance with the seventh embodiment;

Figure 14 shows a flow chart of an example method of authenticating a security document in accordance with the invention;

Figures 15 to 20 show example fibres according to eighth to thirteenth embodiments respectively, the fibres being shown in (a) plan and (b) side view; and Figure 21 shows an example planchette according to a fourteenth embodiment of the invention.

Detailed Description

Figure 1(a) shows a portion of a security document 1 in accordance with a first example embodiment of the invention. The security document 1 comprises a plurality of first phosphorescent regions 2a that emit red visible light when energized, a plurality of second phosphorescent regions 2b that emit blue visible light when energized and a plurality of third phosphorescent regions 2c that emit green visible light when energized. Fig. 1 shows the phosphorescent regions 2 as circular regions spaced apart across the surface of the security document 1, but it will be appreciated that in other embodiments a wide variety of shapes and/or arrangements of phosphorescent regions may be used, with different numbers of types of phosphorescent regions and different colour combinations.

Prior to illumination with a flash the security document 1 appears as shown in Fig. 1(d); the phosphorescent inks in the phosphorescent regions 2 emits substantially no light and accordingly the phosphorescent regions 2 are not visible under visible light and the appearance of the security document is unremarkable.

Fig. 2 shows a plot of emission intensity vs time (the emission decay profde) for the first phosphorescent regions 2a (the line with reference numeral 90), the second phosphorescent regions 2b (the line with reference numeral 92) and the third phosphorescent regions 2c (the line with reference numeral 94). Following illumination with a flash the phosphorescent regions 2 are energised and emit visible light. Over time the intensity of light emitted by a region decays in accordance with the properties of the phosphorescent materials used in its production.

The emission intensity of the third phosphorescent regions 2c (line 94) starts at a lower level and decays more quickly than the emission intensity of the second phosphorescent regions 2b (line 92) and the emission intensity of the second phosphorescent regions 2b (line 92) starts at a lower level and decays more quickly than the emission intensity of the first phosphorescent regions 2a (line 90). At a first time, ti the emission intensity of the first, second and third phosphorescent regions 2a, 2b, 2c is such that all three types of region are visible and the appearance of the security document 1 is as shown in Fig. la. By t2 the emission intensity of the third phosphorescent regions 2c has decayed such that these regions are no longer visible and security document 1 appears as shown in Fig. lb where only the first and second phosphorescent regions 2a, 2b are visible. At the emission intensity of the second phosphorescent regions 2b has now decayed such that these regions are no longer visible and security document 1 appears as shown in Fig. 1c where only the first phosphorescent regions 2a are visible. At ft the emission intensity of the first phosphorescent regions 2a has now decayed such that these regions are no longer visible and security document 1 appears as shown in Fig. Id with none of the phosphorescent regions 2a, 2b, 2c visible and the document appears unremarkable. In some example embodiments, ft may be less than 5 seconds, for example less than 2 seconds, for example less than 1 second after the end of illumination. That is to say, it may take less than 1 second for the emission intensity of all the phosphorescent regions to decay to below visible levels. The period between each of ti and tz.tzand ft, and t and ft may be less than 1 second, for example in the order of milliseconds, for example between 10 and 500 milliseconds.

Thus, the appearance of security documents in accordance with the present example embodiment changes over time in a way that is easy to describe but difficult to reproduce. This change of appearance constitutes a security feature the reproduction of which imposes a burden on counterfeiters.

Figure 3 shows a flow chart of an example method of verifying a security document, for example the security document of the first embodiment. The method comprises illuminating 110 the phosphorescent regions 2a, 2b, 2c of the security document 1 using a flash of visible light, thereby energizing 112 the phosphorescent regions 2 and then capturing a first image 114a of the security document at a time ti after illumination 110 has ended, capturing a second image 114b at later time t2, capturing a third image 114c at yet later time t3 and capturing a fourth image 114d at yet later time ft. As discussed above with reference to Fig. 1 different combinations of phosphorescent regions 2 are emitting 115 visible light at ti, t2,t3, and ft so the appearance of the security document 1 will change as between the first, second, third and fourth images

In some embodiments, the steps of illuminating 110 the regions and capturing the images 114a, 114b, 114c, 114d are carried out using a personal electronic device, for example a smart phone, tablet or similar device. In other embodiments, the steps of illuminating 110 the regions and capturing the images 114a, 114b, 114c, 114d are carried out using a camera with an integrated or separate flash unit. In some embodiments, step 114d may be carried out less than 5 seconds, for example less than 2 seconds, for example less than 1 second after the end of step 110.

After capturing the images 114, the method comprises authenticating 117 the document in dependence on the appearance of the phosphorescent regions in the captured images. Authenticating 117 the document comprises analysing 116 the first, second, third and/or fourth captured images. In some embodiments the step of analysing 116 the resulting images comprises one or more of (i) analysing whether and/or which phosphorescent regions are visible in the captured images, (ii) analysing whether and/or how the appearance of the phosphorescent regions is different as between the captured images, (Hi) comparing the appearance of the phosphorescent regions in the captured images with the appearance in a corresponding series of reference images. If the appearance of the phosphorescent regions is as expected, then the document is taken to be genuine. Likewise, if the appearance of the phosphorescent regions is not as expected, then the document is taken to be not genuine.

In some embodiments a user analyses 116 the images themselves in order to ascertain whether the document is genuine.

In some embodiments, the steps of illuminating 110 the regions and capturing an image 114 are carried out under normal daylight conditions.

In some embodiments a user initiates the sequence of illuminating 110 the regions and capturing the images 114a, 114b, 114c, 144d of the document, for example by providing a command to a software product (e.g. an App) running on a personal electronic device. In the same or yet further embodiments, a software product (e.g. an App), for example on the portable electronic device, may analyse 116 the images (for example using conventional image recognition techniques) and optionally, in dependence on the result of that analysis, provide an indication 124 to a user as to the authenticity of the security document. In some embodiments the software product provides a visual indication regarding the authenticity of the security document, for example using text (e.g. “GENUINE”/ “FAKE”) or colours (e.g. Green and Red) to denote the presence and absence of the phosphorescent regions. In the same or yet further embodiments the software product may provide an audible indication regarding the authenticity of the security document, for example using different sounds to indicate whether or not the document is deemed genuine.

Optionally, the method comprises a user identifying 108 the presence of a phosphorbased security feature in the security document. In some embodiments this comprises a user recognising a visual indicator, for example a symbol 16 (see below) that is visible to a user when the security document is illuminated, for example with visible light. In some embodiments, this comprises the user recognising a coloured region of an inclusion (see below) when viewing the document under visible light. Optionally, the method may comprise a step of downloading 118 a software product, for example an App, configured to carry out one or more steps of the method. In some embodiments, the security document may comprise a machine readable image, for example a QR code, that provides a link to the software product on a remote server, for example an online app store. Thus, in some embodiments the method may comprise a user capturing an image of a machine readable image on the security document and then following various prompts from the portable electronic device to access the remote server and/or download 118 the software product.

Methods in accordance with the present invention may allow a user to authenticate a security document using a phosphorescent security feature thereby increasing the burden on the counterfeiter. Additionally or alternatively, methods in accordance with the present invention may allow for an easy to describe but difficult to reproduce security feature thereby increasing the burden on the counterfeiter. Additionally or alternatively, a wide variety of different effects may be produced by varying the properties of the phosphorescent materials used. Additionally or alternatively, the use of the flash to energise the phosphor and the capture of the image while the phosphor is still highly energized may allow the method to be carried out in normal lighting conditions (i.e. to avoid the need for dark or dim lighting in order for the phosphorescence to be visible to a user), thereby increasing the circumstances in which the verification method can by usefully employed. Additionally or alternatively, such methods may be carried out using a personal electronic device, for example a smart phone, such devices often being carried by private individuals thereby facilitating use of the verification method in a wider range of circumstances. Additionally or alternatively, methods in accordance with the present invention may use a software product to automate aspects of the verification process, for example by analysing the image and providing an indication of authenticity, thereby increasing the ease and/or accuracy of verification.

In some embodiments, users in different categories may use different numbers of images and/or levels of detail of analysis to authenticate a security document. For example a member of the public and an issuing authority may carried out different versions of the above methods. In some example embodiments a member of the public may only capture first and second images (e.g. carry out steps 114a, 114b but not 114c, 114d) after illuminating 110 the regions and/or the analysis 116 carried out by a member of the public may comprise ascertaining that (i) there are some phosphorescent regions visible in the first and second images and (ii) the appearance of the phosphorescent regions is different as between the first and second images. For the same security document, an issuing authority may capture all four images (e.g. carry out steps 114a, 114b, 114c, 114d) and/or the analysis 116 carried out by the issuing authority may comprise comparing the precise combination of phosphorescent regions present in each image with a reference image of the document.

Thus, security documents and authentication methods in accordance with the present invention may allow for different levels of authentication using the same features.

In some embodiments (not shown) two or more phosphorescent regions may overlap so that authentication is based on observing a change in colour between first and second images. For example, a first phosphorescent region that emits red light when energized may overlap with a second phosphorescent region that emit blue light when energized. The overlapping region then appears purple in a first image taken at a first time when both regions are emitting and red in a second image taken at a second time when only the first region remains emitting.

Fig. 4 shows a plot of emission intensity vs time for the three types of phosphorescent regions in a second example embodiment of the invention. In this example embodiment, the emission intensity of the first phosphorescent regions (as shown by line 90) is initially higher than that of the second phosphorescent regions (as shown by line 92) but then decays much more steeply than that of the second phosphorescent regions. Again, the emission intensity of the third phosphorescent regions (shown by line 94) is the lowest initially and fastest decaying. Thus, for the second example embodiment, the visibility of the phosphorescent regions may be summarised as follows: at ti - first, second and third phosphorescent regions visible; at t - first and second phosphorescent regions visible, third phosphorescent regions no longer visible; at T - second phosphorescent regions visible, first and third phosphorescent regions no longer visible; at ti - first, second and third phosphorescent regions no longer visible. Phosphorescent regions in accordance with Fig.4 may be incorporated in a security document as described in connection with Fig. 1 and verified using methods in accordance with Fig. 3.

In another example embodiment (see Figure 5) there is provided a bank note 1 comprising a phosphorescent security feature 12. In other embodiments the security feature 12 may be incorporated into different security documents, for example passports, lottery tickets, certificates, tax stamps, and other items of potentially high value.

The bank note 1 comprises a substrate 52 having a first surface 51 and a second, opposite surface (not shown). The security feature 12 comprises a phosphorescent region 2 provided using a phosphorescent ink that emits green light when energized with a flash of visible light (in some embodiments steps 110 and 112, above). The phosphorescent region 2 is star-shaped. In some embodiments the phosphorescent inks are printed on the first surface 51 and/or second surface of the substrate. In other embodiments, a different machine readable image may be used. In some embodiments coloured inks and/or fluorescent inks are printed on the first surface 51 and/or second surface 52 and define at least in part the geometric shape of the printed region 2. For example, in some embodiments, one half of a star-shaped region is printed in coloured in, and half of a star-shaped region is printed in phosphorescent ink, to form a star-shaped printed region. Similar arrangements of fluorescent, coloured and phosphorescent layers may be provided as discussed below with reference to fibres.

Prior to illumination with a flash (as shown in Fig. 5a), the phosphorescent ink in the star-shaped region 2 emits substantially no light and accordingly the star-shaped region 2 is not visible under visible light and the appearance of the banknote 10 is unremarkable. However, when viewed in an image captured following energization of the phosphorescent ink with a flash, (such an image being shown in Fig. 5(b)) the star-shaped region 2 is visible. In other embodiments the security feature 12 may comprise a region printed with phosphorescent ink of a different colour and/or the security feature 12 may appear as a different symbol, geometric shape, pattern, image or combination thereof. In some embodiments QR code 16 may be used to direct a user (via a personal electronic device) to a software product configured to execute one or more steps of the method described above.

Figure 5(c) shows an image of the banknote 1 being viewed on the screen I l a smart phone 20, the image having been captured at a first time after illumination of the phosphorescent ink using the flash unit (not shown) of the smart phone camera (not shown). The star-shaped region 2 is visible in Figure 2(c).

In some embodiments, a plurality of smaller star shaped regions may be provided.

With reference to Fig. 4, an example method of authenticating the banknote 1 of Fig. 5 comprises capturing a single image 114 at a first time and then analysing 116 that image to determine if the star-shaped phosphorescent region 2 is visible. In the case that the phosphorescent region 2 is visible in the first captured image that bank note is deemed authentic.

In one embodiment, a phosphorescent security feature 12 is provided using a plurality of fibres 260, an example fibre 260 being shown in Figure 6. The fibre 260 comprises a rectangular strip of a substrate 262 having a first surface 261 and a second, opposite surface (not shown). The fibre 260 includes phosphorescent stripes 2 extending across the width of the fibre 260. Each stripe 2 emits red light following energization of the region with a flash of visible light (in some embodiments step 112, above). The fibre shown in Figure 6 is 5mm long and 0.2 mm wide but in other embodiments the length of the fibres may be between 3mm and 10 mm and/or the width of the fibre may be between 0. 125mm and 0.5mm. In some embodiments the substrate is tissue paper or an alternative thin paper. In the present embodiments the phosphorescent regions are in the form of discrete stripes 2. In other embodiments, the phosphorescent regions may cover the majority of the surface area of the first and/or second surface. In the same or yet further embodiments, a phosphorescent region may cover the whole of the first and/or second surface.

Figure 7 shows a bank note 1 comprising a phosphorescent security feature 12 in accordance with an embodiment of the invention. In other embodiments the security feature 12 may be incorporated into different security documents, for example passports, lottery tickets, certificates, tax stamps and other items of potentially high value. A plurality of fibres 260 have been incorporated in the security document substrate 52. Optionally, an alphanumeric code 19, visible in visible light, is printed on the bank note 1. Optionally a QR code or other machine readable element may be provided.

When the fibres 262 incorporated in the bank note 1 are as described with reference to Figure 6, then under visible light and prior to illumination with a flash (as shown in Fig. 7a), the security feature 12 is not visible and the appearance of the banknote 1 is unremarkable. However, when viewed in an image captured following energization of the phosphorescent ink with a flash (as shown in Fig. 7b), the stripes 264 of the fibres 260 emit visible light producing a distinctive visual effect across the surface of the banknote 1.

In some embodiments the fibres 260 are printed with conventional coloured ink(s) that reflect light when viewed under visible light as well as phosphorescent inks and/or comprise a substrate 262 of a different colour to the security-document substrate 52, thereby allowing a user to see the fibres 260 are present in the security document 1. This may facilitate the positioning of the camera with respect to the security document and/or prompt a user that the security feature is present.

Figure 15 shows an example of such a fibre 260 in (a) plan and (b) side view respectively. It will be appreciated that in Figure 15 (b) the thickness of the printed regions has been exaggerated to facilitate this explanation. The fibre 260 comprises a rectangular strip of a substrate 262 having a first surface 261 and a second, opposite surface 263. The fibre 260 includes a phosphorescent region 2 extending across the width of the fibre 260. The phosphorescent region 2 emits yellow light following energization of the region with a flash of visible light (in some embodiments step 112, above). The fibre includes a coloured region 4 extending across the width of the fibre 260. The coloured region 4 reflects blue visible light (i.e appears blue when viewed under visible light). The phosphorescent region 2 and coloured region 4 overlap in an overlap region 6. In Figure 15 the phosphorescent region 2 and coloured region 4 are adjacent and overlap in a central region of the fibre. As shown in Figure 15(b), in the overlap region 6, the coloured region 4 is printed over the phosphorescent region 2. At least part of the phosphorescent region 2 does not overlap with any coloured region 4 on the same side of the substrate 262. Under visible light and prior to illumination with a flash, a user can identify the presence and/or location of the fibres 260 in a security document by looking for the coloured region 4, which will be appear blue. Following energization, the yellow phosphorescent regions 2 of the fibres 260 will emit yellow light. Where the phosphorescent region does not overlap with the coloured region, the fibre will appear yellow. The overlap region 6 will appear green (as the yellow light emitted by the phosphorescent region 2 passes through the blue coloured region 4). The coloured region 4 will appear blue. Thus, when fibres 260 as described in connection with Figure 15 are incorporated in a bank note 1 and viewed in an image captured following energization of the phosphorescent ink with a flash, the emission of visible light from the phosphorescent regions 2 of the fibres 260 produces a distinctive visual effect across the surface of the banknote 1.

Fibres in accordance with the example of Figure 15 are easy to locate (due to coloured region 4) but produce an area of striking illumination (the uncovered portion of the phosphorescent region 2) following energization. The visual effect is made yet more striking and/or difficult to counterfeit by the production of the third colour (in this case green) following energization by mixing the colours of the phosphorescent 2 and coloured regions 4 in the overlap region 6. Additionally, fibres in accordance with the present invention provide a changing colour in the overlap region over time as the emission from the phosphorescent region decays. This provides an additional striking effect that can be used in authentication.

Figure 16 shows a variation of the example fibre of Figure 15. In this example, and in contrast to Figure 15, the phosphorescent region 2 extends across the whole length and width of the fibre 260. The coloured region 4 is provided over a portion of the phosphorescent region 2, such that the overlap region 6 and coloured region 4 occupy the same region of the surface of the fibre. Following energization, the whole of the fibre 260 will appear to change colour as the blue region visible under visible light appears green, and the phosphorescent region 2 not covered by coloured region 4 will appear yellow.

Figure 17 shows a variation of the example fibre of Figure 16. In this example, the phosphorescent region 2 is provided on the first surface 261 of the substrate 262 and the coloured region 4 is provided on the second, opposite, surface 263 of the substrate 262. The substrate 262 is transparent, such that light from the phosphorescent region 2 can pass through the substrate 262 and coloured region 4 and the overlap region 6 appears green when a user views the first surface 261 of the fibre 260 following energization of the phosphorescent region 2. It will be appreciated that this arrangement can equally be used with the fibre of Figure 16.

Figure 18 shows a variation of the example fibre of Figure 15 in (a) plan and (b) side view. In contrast to the example of Figure 15, the phosphorescent region 2 and coloured region 4 do not extend to the ends of the substrate 262. At each end of the substrate 262 there is consequently an unprinted margin 8. The coloured region produced by the phosphorescent region 2 and coloured region 4 is located between the margins. It will be appreciated that such a margin can be provided in any of the fibres of Figures 16 to 18. Advantageously, the use of such margins may increase the margin of error permitted during the cutting process without the appearance of the coloured region being effected.

Figure 19 shows a variation of the example fibre of Figure 18 in (a) plan and (b) side view. In Figure 19, the coloured region 4 extends across the width for the fibre 260 and comprises two parts: a first part 4a that appears blue when viewed under visible light, and a second part 4b that appears red when viewed under visible light. The first and second parts 4a, 4b are adjacent to each other at the centre of the fibre 260. The phosphorescent region is located beneath the coloured region 4 on the substrate 262 and extends further along the length of the fibre 260 than the coloured region 4. Optionally, an unprinted margin 8 is provided at each end of the fibre.

Under visible light and prior to illumination with a flash, a user can identify the presence and/or location of the fibres 260 by looking for the coloured region 4, of which the first part 4a will appear blue and the second part 4b will appear red when viewed under visible light. Following energization, the phosphorescent regions 2 of the fibres 260 will emit yellow light. Where the phosphorescent region does not overlap with the coloured region, the fibre will appear yellow. The overlap region 6 will appear green in the region of the first part 4a of the reflective layer and orange in the region of the second part 5b of the reflective layer (as the yellow light emitted by the phosphorescent region passes through the blue and red ink respectively). Thus, when fibres 260 as described in connection with Figure 19 are incorporated in a bank note 1 and viewed in an image captured following energization of the phosphorescent ink with a flash, the emission of visible light from the phosphorescent regions 2 of the fibres 260 produces a distinctive visual effect across the surface of the banknote 1.

While Figures 15 to 19 have described with reference to phosphorescent regions and visible regions of particular colours it will be appreciated that other colours can be used. The fibres shown in Figures 15 to 19 are 5mm long and 0.2 mm wide but in other embodiments the length of the fibres may be between 3mm and 10 mm and/or the width of the fibre may be between 0.125mm and 0.5mm. In some embodiments the substrate is tissue paper or an alternative thin paper.

In some embodiments (not shown) the phosphorescent regions 2 may also include fluorescent materials that fluoresce under UV with the same colour as the light emitted by the phosphorescent regions 2. This may provide an additional level of security that can be checked using a UV torch, for example to determine that the phosphorescent regions 2 have the same appearance in an image captured following energization of the phosphorescent ink with a flash and under UV light.

Figure 20 shows a variation of example fibre of Figure 19 in (a) plan and (b) side view. In Figure 20, the coloured region 4 has been replaced with a fluorescent region 5 which extends across the width for the fibre 260 and comprises two parts: a first part 5a that appears blue under UV light, and a second part 5b that appears red under visible light. The first and second parts 5a, 5b are adjacent to each other at the centre of the fibre 260. A phosphorescent region 2a, 2b is located on either side of the fluorescent region 5 and emits yellow light after energization. Optionally, an unprinted margin 8 is provided at each end of the fibre. There is no overlap region in Fig. 20.

In use, under UV light the fluorescent regions can be used to locate the fibre. The phosphorescent regions can then be energized and the document authenticated as described above. Neither the fluorescent regions nor the phosphorescent regions are visible under visible light prior to energization of the phosphorescent regions.

Figure 8 shows a flow chart summarising the steps of an example method for producing a fibre in accordance with the invention. The phosphorescent regions 2 are printed 280 on substrate 262, for example using screen printing techniques. The step of printing 280 comprises printing one or more regions with a phosphorescent ink that is visible when viewed in an image captured following energization of the region with a flash of visible light (in some embodiments step 112, above). Optionally, another step of printing 281 is then carried out. The step of printing 281 comprising printing one or more regions with an ink that reflects light of (i.e. appears) a second, different, colour when viewed under visible light. The substrate 262 is then cut 282 into a plurality of fibres 260. Where unprinted margins 8 are provided between the regions, the substrate 262 is cut 282 in the unprinted margins 8. To produce a security document substrate, the resulting fibres 260 are then mixed 284 with a slurry paper pulp, where they form a hydrogen bond with the cellulose fibre in the paper pulp. The paper pulp and fibre mix is then formed 286 into a continuous web of paper which can be used in a security document, for example as the substrate of the security document or as the substrate of a security device affixed to a security document. In some embodiments the paper is used in a banknote, passport, lottery ticket, certificate, tax stamp or other item of potentially high value.

Fig. 9 shows a variation of the embodiment of Fig. 6, in which first phosphorescent regions 2a that emit blue visible light when energized, second phosphorescent regions 2b that emit red visible light when energized, third phosphorescent regions 2c that emit green visible light when energized, and fourth phosphorescent regions 2d that emit yellow visible light when energized are printed on the surface of the substrate 262 of a fibre 260. Each of the first, second, third and fourth phosphorescent regions 2a, 2b, 2c, 2d has a different emission decay profile Figures 9 (a) to (e) show the appearance of the fibre 260 at first, second, third, fourth and fifth times (ti, t2,t3, ft and ts respectively) following illumination of the fibre. Under visible light and prior to illumination with a flash (as shown in Fig. 9e), the phosphorescent regions 2a, 2b, 2c, 2d are not visible and the appearance of the fibre 260 is unremarkable. However, when viewed in an image captured atti following energization of the phosphorescent ink with a flash (as shown in Fig. 9a), all the phosphorescent regions 2a, 2b, 2c, 2d of the fibres 260 emit visible light producing a distinctive visual effect . At t2 (Fig. 9b) all of the phosphorescent regions 2a, 2b, 2d except the third phosphorescent regions 2c are visible. At t3 (Fig. 9c) the second and fourth phosphorescent regions 2b, 2d are visible and the first and third phosphorescent regions 2a, 2c are not visible. At ft (Fig. 9d) the second phosphorescent regions 2b are visible and the first, third and fourth phosphorescent regions 2a, 2c, 2d are not visible. At ts (Fig. 9e) the phosphorescent regions 2a, 2b, 2c, 2d are not visible and the appearance of the fibre 260 is unremarkable. The phosphorescent regions 2 in the embodiment of Fig. 9 are shown as continuous blocks of colour covering the whole of the surface of the fibre 260. In other embodiments the phosphorescent regions may have different shapes and/or arrangements. In the same or yet further embodiments the phosphorescent regions may cover only part of the surface of the fibre, for example with gaps between different types of regions.

Fig. 10 shows the fibres 260 of Fig. 9 embedded in a portion of a substrate 52 of a security document. Such a security document can be authenticated using the method of Fig. 4 or similar methods, the number of images captured being varied in dependence on the number of different types of phosphorescent regions. In some embodiments, the step of analysing 116 the security document comprises checking that the colours visible on the fibres 260 change as expected between different images.

In one embodiment, a phosphorescent security feature is provided using a plurality of planchettes, an example planchette 390 being shown in Figure 11. The planchette 390 comprises a disc of a substrate 262 having a first surface 1 and a second, opposite surface (not shown). In other embodiments the planchette may have a different shape, for example be a different geometric shape (e.g. a triangle, square or rectangle) or a more complex shape. A circular region of phosphorescent ink 2 extends across the majority of the first surface 51 of the planchette 390. In other embodiments, phosphorescent ink may be printed over the whole of the first surface 51 and/or second surface of the planchette 390. The region of phosphorescent ink 2 emits coloured light following energization of the region with a flash of visible light (in some embodiments step 112, above). The planchette shown in Figure 11 measures 3mm in diameter, but in other embodiments the diameter of the planchette may be between 2 mm and 6 mm. When planchettes are incorporated into the substrate of a security document, a striking visual effect is produced, similar to that discussed above with respect to the fibres of Figure 6. The planchettes may be manufactured using a similar process to that described above with respect to fibres (Figure 8).

Figure 21 shows another example planchette 390 in accordance with the invention in (a) plan view and (b) side view. It will be appreciated that in Figure 21 (b) the thickness of the printed regions has been exaggerated to facilitate this explanation. The planchette 390 comprises a disc of a substrate 262 having a first surface 1 and a second, opposite surface 52. In other embodiments the planchette may have a different shape, for example be a different geometric shape (e.g. a triangle, square or rectangle) or a more complex shape. A region of phosphorescent ink 2 extends across the first surface 51 of the planchette 390. The planchette 390 includes a coloured region 4 extending across the first surface 51. The coloured region 4 reflects blue visible light (i.e. appears blue when viewed under visible light). The phosphorescent region 2 and coloured region 4 overlap in an overlap region 6. The region of phosphorescent ink 2 emits yellow light following energization of the region with a flash of visible light (in some embodiments step 112, above). As shown in Figure 21(b), in the overlap region 6, the phosphorescent region 2 is located below the coloured region 4 on the substrate 262. The planchette shown in Figure 21 measures 3 mm in diameter, but in other embodiments the diameter of the planchette may be between 2 mm and 6 mm. When planchettes are incorporated into the substrate of a security document, a striking visual effect is produced, similar to that discussed above with respect to the fibres of Figure 6 and 1 to 20. The planchettes may be manufactured using a similar process to that described above with respect to fibres (Figure 8). Likewise, the variations described in Figures 15 to 20 (e.g. unprinted margins, phosphorescent and coloured regions on different sides of the substrate, fluorescent regions) in connection with fibres may equally be used on planchettes.

In one embodiment, a phosphorescent security feature 12 is provided using a security thread 470, an example security thread 470 being shown in Figure 12 (a) to (d). The thread 470 comprises an elongate strip of a substrate 262 having a first surface 1 and a second, opposite surface (not shown). The thread 470 includes first phosphorescent regions 2a that emit blue visible light when energized, second phosphorescent regions 2b that emit red visible light when energized, third phosphorescent regions 2c that emit green visible light when energized, and fourth phosphorescent regions 2d that emit yellow visible light when energized. The phosphorescent regions are printed on the surface of the substrate 262 and are arranged in a repeating pattern along the length of the thread 470. Each region 2 emits coloured light following energization of the region with a flash of visible light (in some embodiments step 112, above). The thread shown in Figure 12 is 70mm long and 1mm wide, but in other embodiments the dimensions of thread may be between 50 mm and 80mm in length and between 1mm and 5mm wide. In other embodiments, the thread may be replaced with a security stripe, for example a stripe 70mm long and 15mm (although other dimensions may be used) comprising a carrier of between 3 and 8 microns in thickness. In the present embodiments the phosphorescent regions are in the form of discrete stripes 2. In other embodiments, the phosphorescent regions may cover the majority of the surface area of the first and/or second surface. In the same or yet further embodiments, a phosphorescent region may cover the whole of the first and/or second surface.

Figures 12 (a) to (d) show the appearance of the thread 470 at first, second, third, and fourth times (ti, tz, t3, and ft respectively) following illumination of the fibre. Under visible light and prior to illumination with a flash (and/or at a fifth time h being later than the fourth time), the phosphorescent regions 2a, 2b, 2c, 2d are not visible and the appearance of the thread 470 is unremarkable. However, when viewed in an image captured at ti following energization of the phosphorescent ink with a flash (as shown in Fig. 12a), all the phosphorescent regions 2a, 2b, 2c, 2d of the thread 470 emit visible light producing a distinctive visual effect. At tz (Fig. 12b) all of the phosphorescent regions 2a, 2b, 2d except the third phosphorescent regions 2c are visible. At T (Fig. 12c) the first and second phosphorescent regions 2a, 2b are visible and the third and fourth phosphorescent regions 2c, 2d are not visible. At (Fig. 12d) the first phosphorescent regions 2a are visible and the second, third and fourth phosphorescent regions 2b, 2c, 2d are not visible.

Fig. 13 shows the thread 470 of Fig. 12 embedded in the substrate 52 of a security document 1 when all phosphorescent regions 2 are emitting visible light. The thread 470 extends from a first edge 3a of the security document 1 to a second, opposite, edge 53b of the security document 1. The security document 1 may be authenticated using the method of Fig. 4 or similar methods, the number of images captured being varied in dependence on the number of different types of phosphorescent regions. In some embodiments, the step of analysing 116 the security document may checking that the pattern visible on the thread 470 changes as expected between different images.

As discussed above, in some embodiments the phosphorescent security feature 12 may be provided using inclusions, for example fibres (e g. as described in connection with Figs 6 to 10), planchettes (e g. as described in connection with Fig. 11) or other inclusions that are mixed with the pulp used to form a security-document substrate.

Fig. 14 shows a flow chart for an example method of authenticating a security document including security devices as described above and optionally, an alphanumeric code and/or QR code or other machine readable image. The method comprises illuminating 110 the phosphorescent regions 2 to energize 112 the phosphorescent regions 2 and then capturing a first image 114 of the security document at the time ti after illumination 110 has ended but while at least some of the phosphorescent regions 2 are emiting 115 visible light. In some embodiments capturing 114 and illuminating 110 is done using the camera of a smart phone or other portable electronic device. In the same or yet further embodiments further images of the security document may be captured over time, for example as described above in Fig. 3. The method comprises retrieving 120 a previously captured reference image of the security document to be authenticated (this step may be carried out before or after step 114), for example from a remote database. In some embodiments the retrieving 120 is done using a smart phone or other portable electronic device. Optionally, the step of retrieving 120 comprises using 122a an alphanumeric code visible on the security document to locate the reference image in a database and/or following 122b a link, for example provided by a machine readable image, e.g. a QR code, to the reference image in a database. The method comprises authenticating 117 the document by analysing 116 the first image of the security document with respect to the reference image, for example comparing the first image of the security document with the reference image, and authenticating the document in dependence on the degree of similarity between the reference image and the first image. In some embodiments the step of analysing 116 may be carried out (at least in part) by a computer processor, for example a processor of a smart phone or other portable electronic device. Such a comparison can be carried out using conventional image-processing software. In some embodiments, the smart phone or other portable electronic device provides 124 an indication to the user as to the authenticity of the document following the analysis 116. In other embodiments, a user may carry out the analysis step 116 themselves, by comparing the first image to the reference image by eye. Optionally, prior to the capturing 114 of the first image, the method may comprise an issuing authority capturing 130 a reference image of the security document and, optionally, storing 132 said reference image in a database. Optionally, the method may comprise a step of a smart phone or other portable electronic device downloading 118 software to enable the processor of the portable electronic device to carry out one or more of steps 110, 114, 120, 122a, 122b, 116, 117, 124, 130 and/or 132. In some embodiments the step of downloading comprises following a link to a downloadable version of the software on a remove server, for example an app store, for example a link contained in a machine readable image e g. a QR code

Thus methods in accordance with the present example may use the unique distribution of inclusions in the substrate of a security document as a code to verify the authenticity of the security document. Such methods may find particular application when the fibres 260, planchetes 390 or other inclusions are incorporated into the pulp of the security document substrate as the distribution of the inclusions in the pulp is essentially random thereby producing a unique appearance in each document. However, it will be appreciated that such methods are not limited to use with inclusions - for example unique combinations of colours, shapes and/or patterns of phosphorescent regions 2 may be provided the substrate of a security document 1 and/or a security thread 470 thereby providing a visual code that allows authentication of that particular document when compared to a previously-captured image of that document. In some embodiments, a series of images are capture (as discussed above for Figure 3) and compared with a series of previously-captured images of the document taken at the elapsed time following illumination. It will be appreciated that the time dependent nature of the phosphorescent security features described herein lends itself to providing a wider variety of such codes that are visually distinctive yet difficult to reproduce.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. In particular, while the embodiments have been described above in connection with phosphorescent regions it will be appreciated that other afterglow materials (e.g. other materials capable of emitting light following the end of illumination) may be used. For example, some commercially available fluorescent materials may emit light for a very short period following the end of illumination thereby allowing use of such materials in the present invention.

The present invention includes the following aspects/embodiments/features in any order and/or in any combination:

1. A method of authenticating a security document, the security document comprising at least one afterglow region, the method comprising:

- illuminating the security document with a flash of visible light;

- at a first predetermined time after the flash, capturing a first image of the security document; and

- authenticating the security document in dependence on the appearance of the security document in the first image.

2. A method according to any previous and/or following aspects/embodiments/features, wherein the afterglow region is a phosphorescent region.

3. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the security document comprises at least one phosphorescent region of a first type and at least one phosphorescent region of a second type, the phosphorescent region of the first type having a first emission decay profile and the phosphorescent region of the second type having a second emission decay profde, the method further comprising the step of:

- at a second predetermined time after the flash, capturing a second image of the security document; and

- authenticating the security document in dependence on the appearance of the security document in the first and second images.

4. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the method comprises authenticating the security document in dependence on the difference in appearance of the phosphorescent regions of the first and/or second type between the first image and the second image.

5. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the phosphorescent regions of both the first and second type are visible in the first image, the phosphorescent regions of one of the first and second type are visible in the second image, and the phosphorescent regions of the other one of the first and second type are not visible in the second image.

6. A method of authenticating a security document according to any any previous and/or following aspects/embodiments/features, the security document comprising at least one phosphorescent region of a third type and at least one phosphorescent region of a fourth type, the phosphorescent region of the third type having a third emission decay profile and the phosphorescent region of the fourth type having a fourth emission decay profile, the method comprising

- at a third predetermined time after the flash, capturing a third image of the security document;

- at a fourth predetermined time after the flash, capturing a fourth image of the security document; and

- authenticating the security document in dependence on the appearance of the security document in the first, second, third and fourth images.

7. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the method comprises authenticating the security document in dependence on the difference in appearance of the phosphorescent regions between the first, second, third and fourth images.

8. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the method comprises using a personal electronic device, for example a smart phone, to produce the flash of visible light and capture the image(s). 9. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the step of authenticating the security document comprises a user looking at the image(s).

10. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the step of authenticating the security document comprises a computer analysing the image and, in dependence on the appearance of the phosphorescent region in the image(s), providing an indication as to the authenticity of the security document.

11. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the one or more phosphorescent regions comprise printed phosphorescent regions.

12. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the security document comprises a substrate and a plurality of inclusions, for example fibres, planchettes, and/or starlights , incorporated into the substrate, and the phosphorescent regions comprise phosphorescent regions on a first and/or second surface of each of said plurality of inclusions.

13. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the security document comprises phosphorescent regions of a first type and a second type, and the plurality of inclusions comprises a first set of inclusions and a second set of inclusions, each inclusion of the first set having a phosphorescent region of the first type on a first and/or second surface and each inclusion of the second set having a phosphorescent region of the second type on a first and/or second surface.

14. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the security document comprises phosphorescent regions of a third type and a fourth type, and the plurality of inclusions comprises a third set of inclusions and a fourth set of inclusions, each inclusion of the third set having a phosphorescent region of the third type on a first and/or second surface and each inclusion of the fourth set having a phosphorescent region of the fourth type on a first and/or second surface.

15. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the security document comprises a substrate, and the one or more phosphorescent regions are printed on a surface of the substrate.

16. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the security document comprises a substrate and a security thread embedded into the substrate, and the phosphorescent regions comprise phosphorescent regions on a first and/or second surface of the security thread.

17. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, the method comprising authenticating the security document in dependence on whether the appearance of the security document in one or more of the first, second, third and/or fourth images matches that of a previously captured image of the security document.

18. A method of authenticating a security document according to any previous and/or following aspects/embodiments/features, wherein the method comprises obtaining the previous-captured image from a database, for example a database on a remote server.

19. A portable electronic device, for example a mobile phone, having a flash unit and a camera and one or more processors adapted to execute the following steps in accordance with the method of any previous and/or following aspects/embodiments/features:

- illuminating one or more of said afterglow regions with a flash of visible light from the flash unit; and

- capturing the first image of the security document with the camera at the first time after the flash, and optionally;

- capturing the second image of the security document with the camera at the second time after the flash, and optionally;

- providing an indication as to the validity of the security document in dependence of the appearance of the security document in the first image and, optionally, the second image.

20. A computer program product comprising instructions to cause the portable electronic device of any previous and/or following aspects/embodiments/features to execute the following steps in accordance with the method of any previous and/or following aspects/embodiments/features :

- illuminate one or more of said afterglow regions with a flash of visible light from the flash unit; and

- capture the first image of the security document with the camera at the first time after the flash, and optionally;

- capture the second image of the security document with the camera at the second time after the flash, and optionally;

- provide an indication as to the validity of the security document in dependence of the appearance of the security document in the first image and, optionally, the second image.

21. A security document comprising a substrate, the substrate having a plurality of inclusions incorporated therein, each inclusion having a first surface and a second surface opposite the first surface, the first and/or second surface comprising one or more afterglow regions.

22. A security document according to any previous and/or following aspects/embodiments/features, wherein the afterglow regions are phosphorescent regions and the plurality of inclusions comprises a first set of inclusions and a second set of inclusions, each inclusion of the first set having a phosphorescent region of a first type on a first and/or second surface and each inclusion of the second set having a phosphorescent region of a second type on a first and/or second surface, the phosphorescent regions of the first type having a first emission decay profile and the phosphorescent regions of the second type having a second, different, emission decay profile.

23. A security document according to any previous and/or following aspects/embodiments/features, wherein the inclusions are one or more of fibres, planchettes, and starlights.

24. A security document comprising a substrate, the substrate having a security thread incorporated therein, the security thread having a first surface and a second surface opposite the first surface, the first and/or second surface comprising one or more afterglow regions.

25. A security document according to any previous and/or following aspects/embodiments/features, wherein the afterglow regions are phosphorescent regions and the first and/or second surface comprises one or more phosphorescent regions of a first type and one or more phosphorescent regions of a second type, the phosphorescent regions of the first type having a having a first emission decay profile and the phosphorescent regions of the second type having a second, different, emission decay profile.

26. A security document according to any previous and/or following aspects/embodiments/features, wherein the security document comprises one or more indicia, visible in visible light, that indicate the presence of the afterglow regions.

27. A security document according to any previous and/or following aspects/embodiments/features, wherein the security document comprises a machine readable image, for example a QR code, configured to provide a prompt to a user to download the computer program product of any previous and/or following aspects/embodiments/features, and optionally wherein said prompt comprises a link to a remote server, for example an app store via which the computer program product of any previous and/or following aspects/embodiments/features is available.

28. An inclusion for incorporation into a substrate of a security document, wherein the inclusion comprises a first surface and a second surface opposite the first surface, the first and/or second surface comprising one or more afterglow regions and, optionally, the afterglow regions being phosphorescent regions and the first and/or second surface comprising one or more phosphorescent regions of a first type and one or more phosphorescent regions of a second type, the phosphorescent regions of the first type having a having a first emission decay profile and the phosphorescent regions of the second type having a second, different, emission decay profile.

29. An inclusion according to any previous and/or following aspects/embodiments/features, wherein the inclusion is a fibre, planchette, or starlight.

30. A security thread for incorporation into a substrate of a security document, the security thread comprising a first surface and a second surface opposite the first surface, the first and/or second surface comprising one or more afterglow regions and, optionally, the afterglow regions being phosphorescent regions and the first and/or second surface comprising one or more phosphorescent regions of a first type and one or more phosphorescent regions of a second type, the phosphorescent regions of the first type having a having a first emission decay profile and the phosphorescent regions of the second type having a second, different, emission decay profile.

31. A method of authenticating a security document, the security document comprising a document substrate and a plurality of inclusions incorporated into the document substrate, each inclusion comprising: a substrate; at least one phosphorescent region on a first and/or second side of the substrate, the phosphorescent region emitting visible light ; and

(i) at least one coloured region on a first and/or second side of the substrate, the coloured region reflecting light when viewed under visible light, and at least part of said at least one phosphorescent region does not overlap with any coloured region on the same side of the substrate, and/or

(ii) at least one fluorescent region on a first and/or second side of the substrate, the fluorescent region being substantially invisible when viewed under visible light and emitting light when viewed under ultraviolet light, and at least part of said at least one phosphorescent region does not overlap with any fluorescent region on the same side of the substrate; the method comprising:

- illuminating the security document with a flash of visible light;

- at a first predetermined time after the flash, capturing a first image of the security document; and

- authenticating the security document in dependence on the appearance of the security document in the first image.

32. A method according to any previous and/or following aspects/embodiments/features, wherein each inclusion is a fibre, a planchette or a starlight. 33. A method according to any previous and/or following aspects/embodiments/features, wherein the phosphorescent region emits light of a first colour and the coloured region reflects light of a second, different, colour.

34. A method according to any previous and/or following aspects/embodiments/features, wherein each inclusion comprises at least one coloured region on a first and/or second side of the substrate and at least one fluorescent region on a first and/or second side of the substrate, and wherein at least part of said at least one phosphorescent region does not overlap with any coloured region on the same side of the substrate and/or does not overlap with any fluorescent region on the same side of the substrate.

35. A method according to any previous and/or following aspects/embodiments/features, wherein at least one coloured region and at least one phosphorescent region are arranged such that in an overlap region light emitted from the phosphorescent region passes through the coloured region to produce a third, different, colour; and the method comprises authenticating the security document in dependence on the appearance of the overlap region in the first image.

36. A method according to any previous and/or following aspects/embodiments/features, at least one phosphorescent region and at least one coloured region being printed on the same one of the first and second surfaces, at least part of the coloured region being printed over only part of the phosphorescent region to produce an overlap region.

37. A method according to any previous and/or following aspects/embodiments/features, at least one phosphorescent region and at least one coloured region being printed on different ones of the first and second surfaces to produce an overlap region.

38. A method according to any previous and/or following aspects/embodiments/features, wherein the substrate is at least partially transparent in the overlap region.

39. A method according to any previous and/or following aspects/embodiments/features, wherein said at least part of the phosphorescent region which does not overlap with any coloured region on the same side of the substrate and/or which does not overlap with any fluorescent region on the same side of the substrate is in an otherwise unprinted region of a surface of the inclusion.

41. A method according to any previous and/or following aspects/embodiments/features, the inclusion comprising a printed region made up of at least one phosphorescent region and one of both of at least one coloured region and at least one fluorescent region and a first margin, the first margin being an unprinted region of at least one surface of the inclusion, the first margin being adjacent to the printed region and extending between the printed region and a first edge of the inclusion. 42. A method according to any previous and/or following aspects/embodiments/features, the inclusion comprising a second margin, the second margin being an unprinted region of at least one surface, the second margin being adjacent to the printed region and extending between the printed region and a second, different, edge of the inclusion such that the printed region is located between the first and second margins.

43. A method according to any previous and/or following aspects/embodiments/features, wherein the at least one phosphorescent region extends over the entire width of the inclusion and/or the at least one coloured region extends over the entire width of the inclusion and/or the at least one fluorescent region extends over the entire width of the inclusion.

44. A method according to any previous and/or following aspects/embodiments/features, wherein the part of the phosphorescent region that does not overlap with any coloured region on the same side and/or does not overlap with any fluorescent region on the same side extends over the entire width of the inclusion.

45. A method according to any previous and/or following aspects/embodiments/features, wherein the inclusion comprises at least one coloured region, the method further comprising the step of: at an initial predetermined time before the flash, capturing an initial image of the security document; and authenticating the security document in dependence of the appearance of the security document in the initial image and the first image, for example the presence of the coloured regions in the initial image and the presence of the phosphorescent regions in the first image.

46. A method according to any previous and/or following aspects/embodiments/features, wherein the inclusion comprises at least one fluorescent region, the method further comprising the step of:

- capturing an initial image of the security document under ultraviolet light; and

- authenticating the security document in dependence on the presence of the fluorescent regions in the initial image and the presence of the phosphorescent regions in the first image.

47. A method according to any previous and/or following aspects/embodiments/features, wherein the or each phosphorescent region further comprises fluorescent materials in addition to phosphorescent materials and under ultraviolet light said fluorescent materials emit visible light of the same colour as that emitted by the phosphorescent region, the method further comprising:

- illuminating the document with ultraviolet light and - authenticating the document in dependence on the appearance of the document under ultraviolet light and in the first image

48. A method according to any previous and/or following aspects/embodiments/features, comprising using a personal electronic device, for example a smart phone, to produce the flash of visible light and capture the image.

49. An inclusion for incorporation into the substrate of a security document, the inclusion comprising: a substrate; at least one phosphorescent region on a first and/or second side of the substrate, the phosphorescent region emitting visible light; and

(i) at least one coloured region on a first and/or second side of the substrate, the coloured region reflecting light of a second, different, colour when viewed under visible light; and wherein at least part of said at least one phosphorescent region does not overlap with any coloured region on the same side of the substrate; and/or

(ii) at least one fluorescent region on a first and/or second side of the substrate, the fluorescent region being substantially invisible when viewed under visible light and emitting light when viewed under ultraviolet light, and at least part of said at least one phosphorescent region does not overlap with any fluorescent region on the same side of the substrate.

50. An inclusion according to any previous and/or following aspects/embodiments/features suitable for use as the inclusion of any previous and/or following aspects/ embodiments/ feature s .

51. A method of manufacturing an inclusion for incorporation into a security-document substrate, the method comprising the steps of: printing a plurality of phosphorescent regions on a first and/or second surface of a substrate in the form of a sheet, the phosphorescent regions emitting visible light; printing a plurality of coloured regions on a first and/or second surface of the substrate, the coloured regions reflecting light when viewed under visible light and/or printing a plurality of fluorescent regions on a first and/or second surface of the substrate, the fluorescent regions being substantially invisible when viewed under visible light and emitting light when viewed under ultraviolet light; and cutting the substrate to create an inclusion including at least one of the phosphorescent regions and

(i) at least one of the coloured regions and wherein at least part of said at least one phosphorescent region does not overlap with any coloured region on the same side of the substrate and/or (ii) at least one of the fluorescent regions wherein at least part of said at least one phosphorescent region does not overlap with any fluorescent region on the same side of the substrate.

52. A method according to any previous and/or following aspects/embodiments/features, wherein said plurality of phosphorescent regions and coloured regions and/or fluorescent regions are arranged in a plurality of printed regions, each printed region being bounded at least in part by a margin, the margin being an unprinted region of at least one surface of the substrate, the substrate being cut in the margins.

53. A method of manufacturing a security-document substrate, the method comprising the steps of: mixing one or more of the inclusions of any previous and/or following aspects/embodiments/features, or one or more inclusions manufactured using the method of any previous and/or following aspects/embodiments/features with slurry paper pulp such that the inclusions form a hydrogen bond with the cellulose fibre in the paper pulp; and forming the paper pulp and inclusion mix into a continuous web of paper.

54. A security-document substrate containing a plurality of inclusions as claimed in any previous and/or following aspects/embodiments/features or manufactured using the method of any previous and/or following aspects/embodiments/features.

55. A method of authenticating a security document comprising a security document substrate having at least one printed region on a first and/or second side of the substrate, the printed region having a geometric shape, each printed region comprising a phosphorescent region on a first and/or second side of the substrate, the phosphorescent region emitting visible light and each printed region further comprising:

(i) at least one coloured region on a first and/or second side of the substrate, the coloured region reflecting light when viewed under visible light, and within said printed region at least part of said at least one phosphorescent region does not overlap with any coloured region on the same side of the security-document substrate and/or

(ii) at least one fluorescent region on a first and/or second side of the security document substrate, the fluorescent region being substantially invisible when viewed under visible light and emitting light when viewed under ultraviolet light, and within said printed region at least part of said at least one phosphorescent region does not overlap with any fluorescent region on the same side of the security document substrate, and said phosphorescent region and said coloured region and/or said fluorescent region together define the geometric shape of the printed region; the method comprises:

- illuminating the security document with a flash of visible light; - at a first predetermined time after the flash, capturing a first image of the security document; and

- authenticating the security document in dependence on the appearance of the security document in the first image. 56. A security document substrate suitable for use in the method of any previous and/or following aspects/embodiments/features, and optionally having a plurality of said printed regions, each having the same geometric shape, for example a circle, rectangle, triangle, square or star.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.