In computer vision, model conceptions are commonly utilized only at the higher levels of processing. In this article it will be shown that a physically oriented model at the lowest level of processing may serve to gain quantitative statements of recognition performance. To find the limitations of recognition and measurement of occluding edges, a model of their optical properties, in connection with a sensor model was developed. By applying this model conception, without the necessity of referring back to heuristics, it is possible to determine in real images the presence, the position, and the direction of occluding edges, even though if only very small image areas (i.e. 3*3 pixels) are evaluated.