To provide a technology capable of efficiently and accurately associating an image input value with an image colorimetry value.

An image processing system includes: a colorimetry section for generating reference chart colorimetry value data for representing a colorimetry value at a prescribed position of a reference chart; an imaging section for generating reference chart input value data for expressing an input value of the prescribed position of the reference chart; a conversion generating section for generating conversion data denoting conversion from an input value to the colorimetry value; and an input value conversion section for converting object image input value data for expressing an object image input value by using the conversion data. The colorimetry section includes a colorimetry date attaching section for attaching colorimetry date data expressing a colorimetry date to the reference chart colorimetry value data. The conversion generating section includes a current date output section for outputting current date data denoting a present date, and an elapsed days discrimination section for discriminating whether or not the elapsed days from the colorimetry date to the present date is within a prescribed range by comparing the colorimetry date data with the current date data.