1. An image forming apparatus comprising: an image acquisition section that acquires an uncompressed set of image data associated with an identifier specific to a set of image data; an image processing section that interprets print data to extract an identifier given to an irreversibly compressed set of image data contained in the print data, allows the image acquisition section to acquire a corresponding set of image data associated with the extracted identifier and having an image quality equivalent to that of a set of image data before being irreversibly compressed into the irreversibly compressed set of image data, and replaces an image represented by the irreversibly compressed set of image data with an image represented by the corresponding set of image data to generate a print target image; and an image forming section that forms on a recording paper sheet the print target image generated by the image processing section, wherein the irreversibly compressed set of image data and the corresponding set of image data associated with the identifier given to the irreversibly compressed set of image data represent the same object image.