1. An image forming apparatus, comprising: a reading device for capturing image information from original documents; a storage unit for storing received image information; a printing device for executing print jobs on sheets in accordance with image information from the reading device or from the storage unit; and a control processor enabled to function as a job execution unit configured to execute jobs by the printing device whereby input pages of a job-specific input sheet count are formed as output pages of an actual output sheet count less than or equal to the input sheet count; and a log-image generating unit configured to generate log images of the jobs; wherein the log-image generating unit is configured to generate, as a log image, images of a portion of pages among the output pages in a job by the job execution unit, and generate the log image after the job execution unit has terminated execution of the job, the portion of pages being one selected from (1) any specifically designated page or pages among the output pages; (2) a designated proportion of the actually output pages; or (3) output-page mirroring, being a reflection of all actual output pages.