1. A photographic image region extracting apparatus comprising: a scanner portion that includes a bar-shaped light source and that causes the light source to move relative to a photographic sheet on which a photographic image is fixed and to obliquely emit a light to the photographic sheet, wherein the scanner portion reads a light reflected from the photographic sheet and outputs image data corresponding to the photographic sheet; a shadow detecting portion that detects a shadow generated along at least one side of a plurality of sides of the photographic sheet based on luminance information of the image data output from the scanner portion; a photographic sheet extracting portion that extracts a region of the photographic sheet based on the image data output by the scanner portion and the shadow detected by the shadow detecting portion, wherein, if the shadow detected based on the luminance information includes a broken portion wherein a shadow is broken, and if a distance of the broken portion is equal to or smaller than a predetermined value, then the shadow detecting portion carries out a process of interpolating the broken portion to connect the broken shadow; a margin deciding portion that decides whether or not a margin is present at one of the sides of the photographic sheet, which is a side around which a shadow is generated most easily by the light obliquely emitted from the light source, based on image data of the region of the photographic sheet extracted by the photographic sheet extracting portion; and a photographic image extracting portion that specifies a region of the photographic image based on a result of the decision of the margin deciding portion and outputs the specified region of the photographic image.