1. A driving assisting system comprising: an imaging device that is mounted on a vehicle to capture images of a rear region of the vehicle including a blind spot region adjacent to the rear region of the vehicle, the blind spot region being outside of a viewing range of a side mirror, and the blind spot region covering a region closer to the vehicle in comparison with the viewing range; an image processing unit that processes images captured by the imaging device to compress an image region corresponding to the blind spot region on the captured image; and a display device that displays the image processed by the image processing unit in a manner visible to a driver seated in the vehicle, wherein the image processing unit is configured to compress the image region corresponding to the blind spot region such that the ratio of transition of position of the object in the horizontal direction on the captured image at a position within the image region corresponding to the blind spot region to transition of distance from the vehicle to the object is substantially the same as the ratio of transition of position of the object in a horizontal direction on the side mirror at a predetermined region of the viewing range including its horizontal boundary to transition of distance from the vehicle to the object.