The present invention relates to an image forming device using a low visibility information embedding technique to manage a copy history of an original. The image forming device embeds history information with the use of small dots disappearing by copying, and coordinate information on a region embedded with the history information with the use of large dots not disappearing even by copying. Upon first copying, the image forming device newly creates both of the large dot coordinate information and the small dot history information, and embeds them. Upon second or later copying, the image forming device updates the history information having been read out of the original with that on the current copying, and embeds the updated history information in the history information region indicated by the coordinate information.