Abstract: A specific mark adding unit adds a specific mark to a read-in image and a specific mark detecting unit detects the specific mark present in a read-in image. Further, a control unit changes a mode in which a read-in image is duplicated from an ordinary duplicating mode into a specific duplicating mode, the mode changing being made if the specific mark detecting unit has detected the specific mark present in the read-in image. The specific mode comprises a mode in which the read-in image is invalidated in data before being used in the duplicating operation. A unit is further provided causing the specific-mark adding function of the specific mark adding unit either to be activated or not to be activated. A unit is further provided causing the mode changing function of the mode changing unit either to be activated or not to be activated.