1. An image processing system for processing images of a target object located in an environment of a vehicle, the image processing apparatus comprising: a stereoscopic camera comprising: a first camera configured to capture the target object within a first image; a second camera configured to capture the target object within a second image; a computer comprising: an image acquiring unit configured to acquire the first image and the second image; a first sub-image extracting unit configured to extract first sub-images from the first image; a second sub-image extracting unit configured to extract second sub-images from the second image; a matching unit configured to match each pair of the first and second sub-images to determine a degree of similarity between the pair of the first and second sub-images; a similar sub-image setting unit configured to, for each of the first sub-images extracted by the first sub-image extracting unit, set the second sub-image having a highest degree of similarity to the first sub-image, among the second sub-images extracted by the second sub-image extracting unit, to be a similar sub-image corresponding to the first sub-image; and a brightness comparing unit configured to compare in brightness each pair of the first and second sub-images, wherein the matching unit is configured to, if a result of comparison made by the brightness comparing unit between a pair of the first and second sub-images is out of a predetermined brightness range, exclude such a pair of the first and second sub-images from the pairs of the first and second sub-images to be matched; and wherein the first and second sub-images are used by at least one of a travelable zone recognizer and an object recognizer to calculate a distance from the vehicle to the target object based on a difference between a position of a target first sub-image of the first image and a position of the similar sub-image in the second image corresponding to the target first sub image, and wherein a vehicle control is performed by a vehicle controller based on the distance from the vehicle to the target object.