The invention concerns the detection of vehicles in images of a night time scene. In particular, but not limited to, the invention concerns a traffic surveillance system that is used to detect and track vehicles to determine information about the detected and tracked vehicles. Candidate pair of headlights are identified 900 in an image based on luminance of points in the image. These candidates are then verified 902 by identifying 400i a sub-image of the image sized to include a candidate vehicle having the pair of candidate headlights; and determining whether the candidate vehicle is a vehicle represented in the image by testing 400k the sub-image for the presence of predetermined features of a vehicle other than the headlights. Aspects of the invention include a method, software and computer hardware.