In an MFP, an image on an original is read and the image is stored as a document (input image) in an HDD. A marking-information generation module generates marking information (two-dimensional code information) expressing at least one of information relating to storage of the document and an output parameters of the document. A document-relevance-information management module relates the marking information to the stored image, and an encryption/decryption module encrypts the marking information. A marking generation module generates a marking image from the encrypted marking information, and the marking image is printed out.