Mark forming apparatus, image forming apparatus, and mark forming method

An image forming apparatus comprising:

• an image acquisition portion that acquires an image formed on a sheet, the image is formed from a color material which can be decolorized by a decolorizer, wherein the image acquisition portion acquires the image before the decolorizer performs decolorizing;
• a calculation portion that calculates a color material attachment amount of the image from the image acquired by the image acquisition portion;
• and
• a formation portion that forms a different shape based on the color material attachment amount calculated by the calculation portion on the sheet.

A mark forming method of an apparatus printing a mark on a sheet, comprising:

• scanning and acquiring an image formed on a sheet, the image is formed from a color material which can be decolorized by a decolorizer, wherein the image is acquired before the decolorizer performs decolorizing;
• calculating a color material attachment amount of the image from the acquired image;
• detecting a predetermined mark which is already formed on the sheet;
• and
• forming a predetermined mark with a different shape based on the calculated color material attachment amount on the sheet in addition to the detected existing predetermined mark.