1. An image synthesizing device comprising: a plurality of cameras configured to obtain images; and an image processing device configured to receive the images from the cameras, the image processing device being further configured to synthesizes the images of the cameras by determining a plurality of observation points for a reference surface being photographed by the cameras, selecting one of the cameras for each of the observation points as a basis camera such that the basis camera for each of the observation points is the closest of the cameras to the observation points on the reference surface being photographed by the cameras, and designating color and brightness values photographed by the basis camera selected for each of the observation points as color and brightness values for that one of the observation points.