1. An image forming apparatus for processing a plurality of pages having respective original images, comprising: a combining section to create, for each of the plurality of pages, a composite image by combining data of the corresponding original image with data of an additional image such that the additional image is added to the corresponding original image; a log management section to store log information indicative of, for each of the plurality of pages, a combining area of the additional image in the corresponding original image, wherein the log information is created when the composite images are created; a printing section to print the composite images on a plurality of recording sheets respectively; a scanning section to scan the composite images printed on the plurality of recording sheets by the printing section, and obtain composite image data of the composite images; a judgment section to judge, for each of the plurality of recording sheets, whether the respective additional image is overlapped with the respective original image in the respective composite image based on the stored log information and the composite image data obtained by the scanning section; a notification section to notify a judgment result obtained by the judgment section, wherein the notification section notifies the judgment result of those recording sheets of the plurality of recording sheets in which the original image and the additional image overlap each other; and a control section to control the combining section, the printing section, and the scanning section to operate in sequence so that the scanning section operates after the combining section and the printing section.