1. An image reading apparatus for reading a document image represented on a document set on a planar background surface, the image reading apparatus comprising: storage storing a document-image-obtaining application program; an imaging unit configured by the document-image-obtaining application program to generate from the document image a plurality of data images of varying shadow location, by imaging the document image multiple times from mutually differing angles; an image forming unit having processing circuitry configured by the document-image-obtaining application program to function as an image data analysis unit for performing a matching process on the plurality of data images by matching the plurality of data images, on a per-region basis in each of the plurality of images of the document represented by the plurality of data images of varying shadow location to obtain per-region brightnesses for the plurality of data images, and for each matching region comparing the obtained brightnesses to select from among the plurality of data images each data image whose per-region brightness is comparatively brighter and is within a predetermined range defining a shadowless state; and an image compositing unit for using the data images selected on the per-region basis as comparatively brighter and within the predetermined range defining the shadowless state, to generate a composite data image, and for prompting the imaging unit to reimage the document image when for any matching region, none among the plurality of data images has a brightness that is within the predetermined range defining the shadowless state.