1. A vehicle environment recognition system comprising: stereo-image taking means for simultaneously taking images of an environment around a subject vehicle with a pair of cameras and for outputting the images as a reference image and a comparative image; first stereo matching means for calculating first parallaxes or first distances by stereo matching based on the reference image and the comparative image or based on two images formed by subjecting the reference image and the comparative image to a predetermined first preprocessing operation, and for forming a first distance image by assigning the calculated first parallaxes or first distances to pixel blocks in the reference image; second matching means for calculating second parallaxes or second distances by stereo matching based on two images formed by subjecting the reference image and the comparative image to a predetermined second preprocessing operation different from the first preprocessing operation, and for forming a second distance image by assigning the calculated second parallaxes or second distances to the pixel blocks in the reference image; detection means for detecting objects in the reference image on the basis of the first distance image and the second distance image; and selection means for selecting one of a result of detection of the objects based on the first distance image and a result of detection of the objects based on the second distance image.