1. A vehicle warning system, comprising: a first camera mounted on the vehicle at a first longitudinal position along the length of the vehicle, which acquires consecutively in real time a plurality of first camera image frames; a second camera mounted on the vehicle at a second longitudinal position along the length of the vehicle, which acquires second camera image frames; and a processor configured to use information in both first and second camera image frames to determine whether there is a danger of a collision between the vehicle and an object shown in both the first and second camera images, wherein the first and second longitudinal positions are at different positions along the length of the vehicle.