This is pretty much a tracking problem, I would use the open source Predator Tracking algorithm to track each of the car simultaneously. The problem I see is if it is going to be fast enough for 100 cars, but it is worth to investigate it. http://info.ee.surrey.ac.uk/Personal/Z.Kalal/ Alternatively, thinking about using open source-hardware as a solution, use the open source Arduino Micro-controller Piece the sensor you need, and you will have your system at a much lower price ! http://www.arduino.cc/