Head mounted display, motion detector, motion detection method, image presentation system and program

Disclosed herein is a head mounted display including: an enclosure accommodating a presentation section adapted to present a three-dimensional image and located in front of the eyes of a viewer when worn on the head of the viewer; and an imaging element provided in the enclosure and adapted to turn light external to the enclosure into an image, in which the imaging element images light that is vertically downward relative to the enclosure and forward in the direction of line of sight of the viewer when the enclosure is worn on the head of the viewer.