An image processing device is provided which generates an easily reusable electronic document from an input image in which different page sizes are mixed.The image processing device generates a plurality of pieces of display information from a plurality of document images, and, depending on the size and the direction of each of the images, converts the pieces of display information into electronic documents. That is, the plurality of pieces of display information are divided into a plurality of groups, depending on the size and the direction of each of the images, and the display information included in each of the groups is converted into a separate electronic document. Further, sequence information based on the input order of the plurality of document images is stored on an electronic document.