1. A method of detecting a vehicle in an image, the method comprising the steps of: (a) for each point of a set of points of the image, projecting a geometrical model of only a windshield on the image with reference to that point; (b) detecting substantially horizontal edges in the image; (c) determining the probability of each point of the set forming part of a windshield of a vehicle in the image based on correlation of the detected horizontal edges with the horizontal edges of the windshield model referenced at that point; and (d) detecting a vehicle in the image based on a probabilities of neighbouring points.