When an image based on RGB image data accepted by the image processing section and the ICU is to be enlarged by the zoom process section of the ICU (or when specification of an area in an image is accepted by the operation section), the leak-preventing identification mark detecting section, the positional relation calculating section and the forgery-preventing identification mark detecting section respectively determine whether patterns respectively representing a leak-preventing identification mark and a forgery-preventing identification mark are included separately in the entire area of the image and in an area to be enlarged (or an area whose specification has been accepted) or not.