An image forming device is provided which is capable of printing paper fingerprint data encoded into code data on a paper sheet without inducing significant degradation of printing performance due to the slowing of the printing speed. In order to halt paper sheet transport until the processing of sending composite image data, including paper fingerprint data, to a printer has completed, a control component issues to a paper sheet transport control component instructions to halt paper sheet transport temporarily after the scanning of paper fingerprint. The paper sheet transport control component halts paper sheet transport after receiving these instructions. Subsequently, when composite image data is sent to the printer and is ready to be printed on the paper sheet, the control component issues to the paper sheet transport control component instructions to resume paper sheet transport. The paper sheet transport control component resumes paper sheet transport after receiving these instructions.