In this paper, we discuss our verification of the usability of camera images where reference lines are superimposed to enhance the driver's ability to percept the relative distance to other vehicles. A Side View Camera shows images rearward and to the side that include the blind spots of side-view mirrors on an onboard display. It is a system to compensate side-view mirrors, broadening the driver's field of view to eliminate blind spots. However, distance perception based on camera images tends to be different from that based on images of the side-view mirror. This tendency is more noticeable with images taken by a wide-angle camera, and this makes the driver feel uncomfortable. So, in order to eliminate the problem of distance perception based on camera images, we superimposed reference lines on the camera images to assist distance perception, and we verified the usability of this approach. As a result, we confirmed that the Side View Camera, whose images have superimposed reference lines, can assist the driver to more easily judge the relative distance and relative speed.