1. An image-capturing apparatus comprising: an image-acquiring unit which acquires an image that is captured by photographing a photographic subject which is laid on an arbitrary place; a difference image producing unit which produces a difference image between the captured image that is acquired by the image-acquiring unit and an image which is captured before the photographic subject is laid; a contour extraction unit which extracts contour information of the photographic subject from the difference image that is produced by the difference image producing unit; and an image conversion unit which corrects a distortion of the captured image on the basis of the contour information that is extracted by the contour extraction unit.