1. An image processing apparatus comprising: an obtaining section which obtains image data of a first picked-up image and a second picked-up image picked up by an image pickup section; a detection section which detects a brightness change region where brightness changes at predetermined time intervals in the first picked-up image on the basis of the obtained image data of the first picked-up image; a first identification section which performs straight line detection processing on the obtained image data of the second picked-up image to detect a straight line, so as to identify a candidate straight line in a corresponding region corresponding to the brightness change region; and a second identification section which identifies a quadrilateral region including the candidate straight line as an extraction candidate region in the second picked-up image.