1. An image processing device that supplies image data to be used in an image forming apparatus, the image processing device comprising: a data input unit that receives image data; a processor that executes a program stored in a memory to perform operations including: distinguishing, in the received image data, between an overprint region in which overprinting of a coat layer of a transparent material is to be performed on a recording medium and a non-overprint region in which the overprinting is not to be performed; and performing image quality processing to correct the received image data by adjusting a difference in image quality between the overprint region and the non-overprint region by adjusting at least one of a plurality of image quality processing parameters, the image quality processing parameters including a linewidth adjustment parameter and an image contour enhancement intensity parameter; and a data output unit which outputs the image data corrected by the processor.