1. A vehicle-use image processing system which performs image processing on the basis of a road surface image captured by an imaging device mounted on a vehicle, comprising: a reference area setting unit which sets a reference area corresponding to a road surface portion other than a lane mark in the road surface image captured by the imaging device; a histogram preparing unit which prepares a histogram by measuring the frequency of luminance of each pixel of the road surface image in the reference area set by the reference area setting unit; a road surface cluster extracting unit which extracts a cluster of portions, which are equal to or higher than a threshold value in width, height, or area, as a road surface cluster from the histogram prepared by the histogram preparing unit; a lane mark candidate detecting unit which detects a lane mark candidate on the basis of the road surface image captured by the imaging device; a luminance parameter calculating unit which calculates luminance parameters based on the luminance of the lane mark candidate detected by the lane mark candidate detecting unit; and a lane mark detecting unit which detects a lane mark candidate whose luminance parameters calculated by the luminance parameter calculating unit fall within the luminance range of the road surface cluster extracted by the road surface cluster extracting unit as a false lane mark, while detecting a lane mark candidate whose luminance parameters calculated by the luminance parameter calculating unit fall off the luminance range of the road surface cluster extracted by the road surface cluster extracting unit as a true lane mark.