1. A method for determining a threshold for pixel classification in a vehicle occupancy detection system, the method comprising: receiving an IR image of a moving vehicle intended to be analyzed for passenger occupancy in the vehicle, said image having been captured using a multi-band IR imaging system comprising an IR detector and an IR Illuminator, said imaging system having collected intensity values for each pixel in said image; detecting pixels of human tissue of a driver of said vehicle in said IR image; using multi-spectral information of said detected human tissue pixels to determine a pixel classification threshold; and using said threshold to classify human tissue pixels in a remainder of said image.