1. An image forming apparatus comprising: a scanning unit configured to read an original conveyed in the image forming apparatus; an analysis unit configured to analyze a feature value of information about an original image on the original read by the scanning unit; an image generating unit configured to generate an image to be overwritten on the original image with, using image data having the feature value obtained based on an analysis result produced by the analysis unit; an area setting unit configured to set an area on the original image; and an image forming unit configured to overwrite the image generated by the image generating unit in the area set by the area setting unit, on the original image.