1. An image-reading apparatus comprising: an image acquiring unit that causes an image-reading unit to read one or more documents to acquire a read image; an edge detecting unit that detects edge coordinates of a document image closest to an outer edge of the read image in a plurality of certain directions; and a dividing unit that regionally divides the read image in the certain directions based on any one or both of a region of the read image in which no edge coordinates are detected by the edge detecting unit and the edge coordinates of an edge end of the document image detected by the edge detecting unit.