The present invention provides a technique relating to image processing capable of searching for, from a surface of paper, a more suitable region for matching of paper fingerprint information or print paper surface unique information. Its configuration includes a region dividing section for dividing image data including a read out paper fingerprint into a plurality of regions; a section for obtaining variance of gradation values of pixels in the individual regions divided by the region dividing section; a deciding section for making a decision from each variance value obtained by the section for obtaining variance of gradation values as to whether a corresponding region is suitable for matching of the paper fingerprint information; and an extracting section for extracting the paper fingerprint information in the region decided by the deciding section.