In a mobile terminal apparatus, a user identifying unit (a) extracts a printed matter image of a printed matter in a photo image taken by an imaging device, (b) transmits to an image forming apparatus a user inquiry with the printed matter image, (c) receives a response to the user inquiry from the image forming apparatus, and (d) displays the photo image on a display device and displays the user name indicated by the response so as to accompany the printed matter image in the displayed photo image. In the image forming apparatus, a printed matter history managing unit determines a document image that agrees with a printed matter image on the basis of a printed matter history upon receiving the user inquiry and the printed matter image, and transmits as the response a user name of a user associated with the determined document image.