Additional data is embedded in a printed image in a way that makes the
additional data unrecognizable to eyes and recognizable without fail by an image
input apparatus. An image processing apparatus of the present invention has: an
average calculation unit as a density value detection part that detects the density
value of a predetermined color component of image data representing a nearby image
in the vicinity of an image to which additional data is to be added; a pattern
selection unit that decides a pattern which is larger in area at the larger density
value detected by the average calculation unit and has a shape corresponding to
the value of the additional data to be added to the image; and an addition processing
unit that superimposes the pattern decided by the pattern selection unit on image
data representing the image.
