In a copying operation, an MFP reads a code image printed on the paper, acquires a paper ID from the code image, acquires paper information associated with the paper ID, specifies an electronic document as a print source, and acquires the specified electronic document. The MFP prints a paper ID on the paper with the code image and the acquired electronic document, and stores paper information including a paper ID of a copy source in association with the paper ID. When a first MFP leaves an image processing system, respective information concerning electronic document acquisition managed by the first MFP is transferred to a second MFP.