An image forming apparatus has an image data reading section that reads image data formed on a document, an image processing section that separates regions where effective information is present from the read image data so as to determine, for every separated region, a shape of a see-through preventing pattern and a position at which the see-through preventing pattern is formed, and an image printing section that prints the determined see-through preventing pattern at a part on a back surface of a recording sheet on which the document is printed, on the basis of the information of the determined position at which the see-through preventing pattern is formed, the part corresponding to any of the regions where the effective information of the document is present.