1. An output image data generating device that generates output image data from multiple objective image data and ornamental image data according to layout control information, wherein the layout control information specifies layout locations and layout dimensions of the multiple objective image data to be laid out on the ornamental image data, said output image data generating device comprising: an image data acquisition module that obtains the multiple objective image data; a ornamental image data acquisition module that obtains one or plurality of the ornamental image data; an image analysis module that analyzes each of the obtained multiple objective image data; a layout location assignment module that allocates the multiple objective image data to plural layout locations included in the obtained ornamental image data, based on a result of the analysis; and an output image data generation module that generates output image data from the multiple objective image data and the ornamental image data, according to the layout control information and the allocation of the respective objective image data to the plural layout locations.