1. An image forming apparatus comprising: a scanning unit configured to read the recording material conveyed in the image forming apparatus; a specifying unit configured to specify an area in which an image is formed, in a recording material read by the scanning unit; and an analysis unit configured to analyze a feature value of information about an image formed on the recording material read by the scanning unit, wherein the analysis unit further divides information contained in the specified area into individual items of information, calculates vertical and lateral lengths per a unit of information as a size of the unit of information; overwriting image generating unit configured to generate an overwriting image based on the size of the unit of information for individual items of information analyzed by the analysis unit; an image forming unit configured to overwrite the overwriting image on the image formed on the recording material in the area specified by the specifying unit, wherein the overwriting image is formed as an area having a predetermined ratio to the area specified by the specifying unit, and wherein the overwriting image is formed by one or more images chosen among plural images, the one or more images being chosen so that the predetermined ratio is more than 50 percent.