1. A system comprising: a first camera mountable on a vehicle; a second camera mountable on the vehicle behind the first camera; and a processor operatively connected to said first and second cameras, wherein said processor is adapted to acquire a first image frame from said first camera and to acquire a second image frame from said second camera; wherein said processor is configured to locate a first feature of a first image of an object in the first image frame and a second feature of a second image of said object in the second image frame and determine alignment thereby of the first and second image frames, wherein respective locations of the first feature in the first image frame and the second feature in the second image frame are responsive to respective positions of the second camera behind the first camera, and wherein said processor is configured to compute a distance between said vehicle and said object based on said alignment.