Stored digital data is searched for on the basis of an input image, difference information is extracted by comparing the retrieved digital data and the input image, and the difference information is composited to the digital data. Digital data generated by composition is stored. When no digital data is retrieved, the input image is converted into vector data, and the image that has been converted into the vector data is stored as digital data. Obtained region segmentation information and an input image are composited, the composite image is displayed on an operation screen of an MFP, and a rectangular block to be vectorized is designated as a specific region from the displayed region segmentation information. A user designates the specific region by designating rectangular blocks in an image using a pointing device.