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 secondary camera adapted for mounting inside the vehicle, wherein said secondary camera is adapted to focus on at least a portion of the surface of the window and acquire a secondary image of the at least one obstruction when present on the surface; and a processor adapted to process said secondary image and for classification of the at least one obstruction; and a primary camera adapted for mounting inside the vehicle, wherein the primary camera is configured to acquire a plurality of primary images of the environment through the window, wherein a region of the window is subtended by respective fields of view of said secondary camera and said primary camera, and wherein said processor is configured to process at least one of said primary images and to trigger said classification of the at least one obstruction responsive to deterioration of image quality in at least one of said primary images.