In the present invention, paper fingerprint information of a document is read (step 801) and whether the paper fingerprint information is registered is judged (step 802). If it is judged that the paper fingerprint information is registered, read image data are acquired (step 814). Super-resolution processing is then applied to the read image data and read image data, which had been acquired from the document up to a previous time, and high-resolution image data are thereby acquired (step 816). Next, paper fingerprint information of a recording sheet is read (step 808), and the paper fingerprint information and added information, including information indicating a storage location of the read image data that have been acquired up until now in regard to the document, are stored in an associated manner (step 810). An image is then formed on the recording sheet based on the high-resolution image data (step 812).