1. An image processing device configured to generate and output composite data in which two or more document images are combined, comprising: an area detecting unit configured to detect allocation areas from template data that defines the allocation areas where the document images are to be allocated on the composite data, respectively; an area position specifying unit configured to specify a position of each of the detected allocation areas with respect to a first standard for defining a position on the template data; an area identification providing unit configured to provide an area identification to each of the allocation areas based on the specified position of each of the allocation areas; an image acquiring unit configured to acquire image data based on document sheets set thereon on which the document images to be combined are formed; an image extracting unit configured to extract the document images from the acquired image data; an image location specifying unit configured to specify a location of each of the extracted document images with respect to a second standard for defining a location on the acquired image data; an image identification providing unit configured to provide an image identification to each of the document images based on the specified location of each of the document images; an allocation area identifying unit configured to identify an allocation area corresponding to each of the document images based on the image identifications and the area identifications; an image editing unit configured to edit each of the document images so as to be allocated in the corresponding one of the allocation areas that is identified by the allocation area identifying unit; a composite data generating unit configured to generate the composite data in which the edited document images are allocated in the respective allocation areas; and an output unit configured to output the composite data generated by the composite data generating unit.