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; and using multi-spectral information of said detected human tissue pixels to determine a pixel classification threshold C th comprising: 
 C th =C m −βV c , where C m is a mean of correlation coefficient values of pixels of said driver's detected face, V c is a variance of said correlation, and β is a constant.