An apparatus (20) for determining a location of a person's head (90) includes stereo vision system (60) for imaging an area of interest such as the interior of a vehicle (26). The vision system provides an image signal of the area of interest. An analyzer (80) analyzes the image signal to identify head candidates (90', 210, 212, 214, 216) in the area of interest and provides data regarding any identified head candidates in the area of interest. A processor (80) processes the provided data regarding identified head candidates to locate the person's head. In an air bag restraining system (22), a controller (50) monitors the location of the person's head and controls an air bag (34) in response to a sensed crash condition (52) and the location of the person's head.