Motion of one or more physical objects relative to a display surface of a display system is detected and an optical flow determined from the motion is used to manipulate a graphical object presented on the display surface. The one or more physical objects are detected in response to light reflected from...http://www.google.co.uk/patents/US20060284874?utm_source=gb-gplus-sharePatent US20060284874 - Optical flow-based manipulation of graphical objects
