1. An image processor comprising: a visual point conversion section respectively converting images photographed by an n-number of photographing apparatuses (where n is an integer of 2 or larger) into bird's-eye view images as viewed from a virtual visual point; and an image synthesis section synthesizing the obtained bird's-eye view images to generate a synthetic bird's-eye view image, and generating a video signal for displaying the synthetic bird's-eye view image on a display device, wherein the image synthesis section compares, between a plurality of the bird's-eye view images, images of a common region where the plurality of the bird's-eye view images overlap upon the synthesis to thereby specify a difference region between the plurality of the bird's-eye view images in the common region, selects, in accordance with position of the difference region in the common region, one bird's-eye view image from among the plurality of the bird's-eye view images as an image to be adopted, and adopts, as an image of the common region in the synthetic bird's-eye view image, the image of the common region in the image to be adopted.