A system includes a receiving unit and a controller. The receiving unit receives data about the number of processes performed in an image forming unit to form an image with a decolorable color material and data about the number of processes performed in a decolorizing unit to decolorize an image formed with the decolorable color material. Based on the data received by the receiving unit the controller calculates the number of media in user's use in a condition after they are subjected to image formation by the image forming unit and before they are decolorized by the decolorizing unit. The controller deters image formation by the image forming unit if the number of the media in user's use exceeds a first threshold, and allows the image forming unit to form an image if the number of the media in user's use does not exceed the first threshold.