1. An image processing method comprising the steps of: imaging an inspection object moving in a predetermined direction a plurality of times with an imaging unit disposed in a predetermined position while a visual field of the imaging unit is lighted by a lighting source disposed in a constant relative position with respect to the imaging unit; aligning a plurality of images with the inspection object as a reference by searching sequentially a region indicating at least part of the inspection object between the two images in the plurality of images acquired by a series of imagings with the imaging unit; and producing a composite image from the aligned plural image, wherein the producing the composite image comprises a step of computing image information representing a unit region from pieces of image information possessed by regions in the plurality of aligned images, wherein the step of computing is performed in each unit region constituting the composite image, and wherein the image information corresponds to the unit region.