1. An image processing device that supplies image data to be used in an image forming apparatus, the image processing device comprising a control unit configured to process the image data in accordance with an image quality processing parameter, wherein the control unit distinguishes between an overprint region in which overprinting of a coat layer of a transparent material is to be performed on a transfer medium and a non-overprint region in which the overprinting is not to be performed, and adjusts a difference in image quality between the overprint region and the non-overprint region by using the image quality processing parameter.