1. An image processing device configured to generate and output composite data in which two or more images are combined, comprising: an image acquiring unit configured to acquire image data of one or more document sheets in a single acquiring operation; an image extracting unit configured to extract, from the acquired image data, document images respectively based on the document sheets; an image position specifying unit configured to specify a position of each of the extracted document images which position is defined on the acquired image data; a first identification providing unit configured to provide each of the document images with a first identification for identifying the document image, based on the specified positions of the document images; an input unit configured to input data for creating one or more ancillary images; a second identification providing unit configured to provide each of the ancillary images created based on the input data with a second identification for identifying the ancillary image; an ancillary image identifying unit configured to identify one of the ancillary images as being associated with one of the document images, based on the first and second identifications; a composite data generating unit configured to generate one or more pages of composite data, each page of the composite data containing one or more combinations each of which includes one of the document images and an ancillary image identified by the ancillary image identifying unit as being associated with the one of the document images; and an output unit configured to output each page of the composite data generated by the composite data generating unit.