1. A vehicle surroundings awareness support device comprising: an image reception unit that receives captured images comprising a plurality of frames taken sequentially by an onboard camera for imaging the surroundings of a vehicle; an optical flow computation unit that computes an optical flow on the basis of feature points contained in the plurality of frames imaged at different times; a moving object detection unit that detects a moving object in the surroundings of the vehicle on the basis of the optical flow; and a superimposing unit that superimposes a display for showing a movement trajectory for the moving object, in a direction opposite to a moving direction of the moving object, onto the captured images, on the basis of the optical flow, and further comprising: an afterimage generation unit that sets an image region containing at least some pixels constituting the moving object as a designated image region in a designated frame, which is one of the frames constituting the captured images, and that generates an afterimage using the pixels of the designated image region, wherein: the superimposing unit imparts the frames following the designated frame with predetermined weightings and superimposes the afterimage thereon, the predetermined weightings being progressively decreased as the afterimage is moved away from the moving object.