1. An occupant sensing system comprising: an illuminating element for selectively illuminating the interior of a vehicle; an image sensor for acquiring a first image of the interior of the vehicle when the interior of the vehicle is illuminated by ambient sources only and for acquiring a second image of the interior of the vehicle when the interior of the vehicle is illuminated by ambient sources and said illuminating element; and a controller for removing the effect of ambient sources by comparing said first and second images thereby producing a third image of the interior of the vehicle as illuminated by the illuminating element only, said controller determining the presence of an occupant by comparing said third image to a produced map of the interior of the vehicle.