1. A method for identifying a location of an object in a physical scene with a stereo camera comprising: identifying a virtual surface in the physical scene; constructing an approximate disparity set for the virtual surface; acquiring a main and a reference image of the scene with the stereo camera; warping the reference image according to the disparity set; subtracting pixels of the warped reference image from corresponding pixels of the main image to determine a depth residual of each pixel; and identifying pixels having a substantially non-zero residual with a surface of the object not coincident with the virtual surface.