1. An image forming apparatus, comprising: a communication section that receives a first print data and attribute information specific to a specific graphic form; a rendering section that renders an image from the first print data; a background separation section that separates the specific graphic form from a background in the rendered image and outputs a visual image of the specific graphic form; a specific graphic form storage section that stores the output visual image of the specific graphic form and the received attribute information specific to the specific graphic form as a reference image and reference attribute information, respectively; an image determination section that: determines at least one of (i) whether or not an image matching with the reference image is included in target data and (ii) whether or not an image having the reference attribute information is included in the target data; and detects the image identified through the determination as an image corresponding to the specific graphic form; and a color conversion processing section that performs specific color conversion processing for the image corresponding to the specific graphic form.