Abstract: The invention extends to a tracking device for tracking a position of a moving object such as a human head or eyes, the device comprising a camera, a radiation source radiating electro-magnetic radiation, and a processor for calculating variables indicative of the position of an object relative to the camera, wherein the camera is adapted to capture images using illumination provided by the radiation source, wherein the radiation source comprises a source of infrared radiation and the camera comprises a monocular image input. Further aspects of the invention relate to an associated method for tracking a moving object; to quickly sorting a set of competing models of the users head; the use of threshold conversion to distinguish characteristics of captured images, and controlling the output of a three dimensional display in dependence on the tracked position of a user's head.