An image processing apparatus: detects an object position included within an overlapping region of a first image corresponding to a vehicles's traveling direction and a second image corresponding to a direction crossing the traveling direction; assigns the first image a first value when the object is in a first position, and a second value smaller than the first value when the object is in a second position more distant from a traveling direction axis of the vehicle than the first position, and assigns the second image a third value when the object is in the first position, and a fourth value larger than the third value when the object is in the second position; and determines a boundary so that the object is included within an image having a larger value than the other; and joins the first and second images.