1. An image processing apparatus comprising: an image acquiring device which sequentially acquires images that are captured in a continuous manner; a face detecting device which detects a face in the acquired images; an expression change amount calculating device which calculates an expression change amount representing a change in expression between a face detected in an image of a current target frame and a face detected in an image of a previous target frame, for each of the target frames, the target frames being every acquired frame or frames at a regular interval in the acquired frames; an extracting device which extracts an image of a target frame for which the calculated expression change amount is greater than or equal to a predetermined value; and a storage device which stores in a storage medium the image of the extracted target frame or an image of a frame near the extracted target frame.