Patent ID: 8306319

Claim:
A sheet identifying apparatus, comprising: a reading section that reads a sheet on a pixel basis of a predetermined area as a unit including color information having a brightness; a storage section that stores image data including a plurality of pixels read by the reading section; an increasing/decreasing section that acquires moire data specific to increasing or decreasing ratios, for the image data stored in the storage section, by increasing/decreasing a number of the pixels of the image data according to the increased or decreased ratios; and a sheet identifying section that identifies authentication of the sheet based on the moire data of the image data acquired by increasing/decreasing the number of pixels by the increasing/decreasing section, wherein the increasing/decreasing section increases/decreases the number of pixels with different ratios respectively in a sheet capturing direction and in a direction perpendicular to the sheet capturing direction such that the ratios in the two directions are different from each other by at least a factor of two.