1. An image processing apparatus comprising: means for inputting a plurality of frame images serving as video images; means for detecting, from each frame image in the plurality of frame images, a straight-line component in a specific direction; means for generating an obstacle candidate area as an image area in a vicinity of the detected straight-line component; means for tracking the obstacle candidate area in an image succeeding each frame image in the plurality of frame images, and producing a tracking result for the obstacle candidate area; means for determining, using the tracking result of three or more obstacle candidate areas, whether the three or more obstacle candidate areas belong to a specific plane and producing a determination result; and means for detecting an obstacle based on the determination result.