1. A system mounted on a vehicle for classifying at least one obstruction on a surface of a window of the vehicle, the system comprising: (a) a secondary camera mounted inside the vehicle, said secondary camera focusing on at least a portion of the surface of the window; and (b) a processor which processes a plurality of secondary images acquired by said secondary camera, and identifies the at least one obstruction when present on the surface; wherein the surface of the window can be selectably either the external surface of the window or the internal surface of the window.