The present invention refers to a security feature for use in security documents, a method for document authentication and a method to combat the falsification of security documents by the monitoring of the counterfeits.

Many security features are already used in graphic arts, that try to prevent or make more difficult a counterfeiter's job in unauthorized document reproduction. The existing security features work, usually, like the following: they are elements of hard execution, fabricated by machines and techniques of high complexity and sophistication, unavailable to the general public, which make these elements, in theory, copy-proof. The existing security features work, thus, in a preventive way, discouraging forgery through the insertion of deterrents or difficulties to its achievement.

However, due to modern computing expedients, the drop in prices of graphic technologies and, as a result, their availability, resources like scanners, high definition printers, graphic editors etc, are becoming more and more affordable. In this present-day environment, though it's still impossible to accurately reproduce the expensive and sophisticated security features, excellent simulations of them can be found, absolutely capable of deceiving the common citizen. Thus, even if the conventional security features keep being used to discourage criminal action, it's necessary to admit that there is currently no fraud-proof security feature. Considering this problem and with the aim at solving it, the present security features has been conceived, seeking to combat counterfeiting, not in a preventive way anymore, but in a reactive way, supporting inhibitory measures to be taken by the competent authorities

5 after the commission of the crime, as will be shown as follows.

Many countries which are concerned about the protection of their security documents have been developing different systems for counterfeit monitoring. In brief, they are databases where relevant information about seized counterfeits is stored. Through data comparison

JLO it's possible to come to helpful conclusions like, for example, the identification of counterfeit families. Amongst the information to be stored, are rather searched those peculiarities capable of unequivocally binding the counterfeits to each other, linking them to a common origin. For this purpose, it's necessary to identify and store the recurrent characteristics of

15 all members of a counterfeit family.

The present invention suggests the inclusion in the security document of a "Varying Position Print", which means: a graphic element with a different position in each produced document. The protection of the security document occurs like the following: during the scanning of the

20 original document, the position of the "Varying Position Print" is captured and will be repeated in all reproduced document. That's because in this process the image of the "Varying Position Print" and the image of the rest of the document are saved together, in the same digital file. So, every counterfeit produced from that same file will bring a reproduction of the

25 "Varying Position Print" occuring, invariably, in the same position, which will serve as a linking element to the identification of the counterfeit family. An evidence of forgery will be, so, the always constant position of this element that should normally have a varying position. The same works if a photographic reproduction process is used.

For easiness, the present invention can be used in combination with another security feature, called "Monitoring Ruler" (see

WO/2008/074106), in order to register the position of the "Varying

Position Print" without the necessity of an external measurement tool and free from casual deformations that may occur during counterfeit printing or cutting steps. That's because these eventual deformations will occur with the same intensity upon both "Varying Position Print" and "Monitoring

Ruler" reproductions, preserving their relative position, what would not happen if one uses an external ruler.

The present invention also refers to a "Method for Document Authentication", based on a consistence test to be performed between the "Varying Position Print" and the variable data set of the security document.

The present invention also refers to a "Method for Counterfeit Monitoring", based on the storage and comparison of information obtained from each "Varying Position Print" reproduction, found in the counterfeits.

The description below and the associated figure, as non- limitative example, will make the invention clear.

Fig. 1 is a sketch of a security document (4), oriented in relation to horizontal (1) and vertical (2) axes, equiped with three "Varying Position Prints" (5), two "Monitoring Rulers" (6) (see WO/2008/074106) and a variable data set, in the form of text (7) and stored in a security chip (8). The first "Varying Position Print" has as motif the figure of a "hand", the second has as motif the figure of a "star" and the third one the figure of a "cross".

5 According to what the figure illustrates, the proposed security feature (5) is characterized by a print (5) with varying position, in relation to horizontal (1) and vertical (2) axes, in each produced document (4).

The position of the security feature (5) on the security "10 document (4) can be defined by following rules:

- position calculated by aleatory function: in this case, the horizontal (1) and vertical (2) coordinates of the "Varying Position Print" (5) are calculated by an aleatory number generator algorithm;

- position calculated by hash function: in this case, the 15 horizontal (1) and vertical (2) coordinates of the "Varying Position Print"

(5) are calculated by hash functions applied to the variable data set (7 and 8) of the security document (4).

The proposed security feature (5) can be constituted by different motifs: dots, strokes, letters, numbers, graphic symbols, drawings, 20 images, geometric figures or even barcodes or other form of graphic representation of data.

The motif to be used in the security feature (5) can be defined by following rules:

- preset motif: in this case, the motif to be used in the 25 "Varying Position Print" is fixed and defined by the document issuer; - motif selected by aleatory function: in this case, the motif to be used in the "Varying Position Print" (5) is variable and selected by an aleatory number generator algorithm;

- motif selected by hash function: in this case, the motif to be used in the "Varying Position Print" (5) is variable and selected by a hash function applied to the variable data set (7 and 8) of the security document (4).

The variational possibilities of the proposed security feature

(5) don't need to be restricted to position or motif characteristics, and can be extended to color and size characteristics, which can also be selected by aleatory or hash functions applied to the variable data set (7 and 8) of the security document (4).

To aggregate more safety to documents equiped with "Varying Position Print" (5), the issuer can opt for producing entirely individualized documents, in other words, with a particular combination of characteristics - positions, motifs, colors and sizes - unique and exclusive for each produced document (4). For this solution it is necessary the use of a database, which will store all combinations already in use, and each new generated combination must be inserted in this database, after the checking that there is no other document with the same characteristics.

The proposed security feature (5) can be produced by any process of variable information printing, like: dot matrix printing, ink-jet printing, laser printing, digital offset, laser engraving, etc. The proposed security feature (5) can be printed directly on the final support (4) or on intermediate support (not represented), to be later attached to the final support of the security document (4).

For a dissembling use of the proposed security feature, it is recommended the adoption of small sized "Varying Position Prints" (5).

About the proposed "Method for Document Authentication", it is based on a consistence test to be performed between the "Varying Position Prints" (5) and the variable data set (7 and 8) of the security document (4). For the application of said "Method for Document Authentication" it is necessary that the "Varying Position Prints" (5) have been produced with such characteristics - positions, motifs, colors and sizes - selected by hash functions applied to the variable data set (7 and 8) of the security document (4). The method works like the following:

- for each questioned document (4), hash functions are applied to the variable data set (7 and 8);

- with the so obtained values one can discover which would be the caracteristics - position, motif, color and size - of the "Varying Position Print" (5) of an authentic document;

- the so obtained characteristics are then compared with the caracteristics - position, motif, color and size - of the "Varying Position

Print" (5) found in the questioned document (4);

- in case of perfect conformity, the variable data set (7 and 8) is reliable;

- in case of unconformity, the questioned document (4) has suffered some kind of adulteration. About the proposed "Method for Counterfeit Monitoring", it is based on the storage and comparison of information obtained from each "Varying Position Print" reproduction (5), found in the counterfeits (4). The method works like the following: - for each seized counterfeit (4), its general information

(model, numbers, issuer identification, manufacturer identification, signatures identification, etc) and its variable data set (7 and 8) are stored in a database;

- for each "Varying Position Print" reproduction (5), its characteristics - position, motif, color and size - of occurrence in the counterfeit (4) are extracted and also inserted in the database;

- through the comparison of stored information, correlations among the seized counterfeits can be established, in order to identify same origin counterfeits, in higher or lower probability, calculated over the quantity of coincident characteristics and their frequency of occurrence in the universe of authentic documents.

It's notorious that a counterfeiter's attack has always the variable data set (7 as 8) as primary target. By this practical observation, the proposed security feature (5) aims at spreading the document surface (4) with other identifying characteristics, also variable, but less attractive to countefeiter's attention.

Depending on the extent of the counterfeiter's attack upon the "Varying Position Prints" (5), it will be possible to reliably monitor the counterfeits and, in some cases, even discover which was the authentic document used as a model to the counterfeit (in case of individualized document producing).

By the analysis of the application example of Fig. 1, it's possible to observe that the first "Varying Position Print" (5), with the motif of a "hand", is positioned on coordinates {4,18}. The second

"Varying Position Print" (5), with the motif of a "star", is positioned on coordinates {8,5}. The third "Varying Position Print" (5), with the motif of a "cross", is positioned on coordinates {27,4}, in relation to the

"Monitoring Rulers" (6) (see WO/2008/074106) and to horizontal (1) and vertical (2) axes respectively.

According to the proposed "Method for Document

Authentication", the hash functions must be applied to the variable data set

(7 and 8) of the security document (4). If the so obtained result is "hand" in

{4,18}, "star" in {8,5} and "cross" in {27,4}, the variable data set (7 and 8) is reliable.

Supposing now that the questioned document (4) is a counterfeit. According to the proposed "Method for Counterfeit Monitoring", the characteristics - positions, motifs, colors and sizes - of each "Varying Position Print" reproduction (5), must be stored in a database - in this example: the motif of a "hand" associated to coordinates {4,18}, the motif of a "star" associated to coordinates {8,5} and the motif of a "cross" associated to coordinates {27,4}.