Expounding on my AS3 webcam motion detection experiments I've designed and built a prototype for an installation that allows a person to draw on a wall using their limbs.
The concept is to allow human interaction to affect physical space, freeing oneself from all traditional user interface. The application works by constantly monitoring a webcam, taking snapshots of each frame. Those frames are then constantly drawn to a bitmap data object. Then each pixel in each frame is monitored by comparing the pixels in the current frame to the pixels in the previous one. The difference in brightness within each section determines whether or not motion had occurred in this area of the screen. If motion is detected the coordinates of a rectangular grid around said motion is recorded and the drawing begins. To slow down the drawing I draw at the x and y coordinates of the white ball which is tweened with easing rather than drawing directly where there are points of motion.

Thanks to steve for filming and editing this video, asluv for the laser drawing class and NORTH for being forward thinking enough to encourage digital experimentation.

You can try the experiment small scale and online here: AS3 webcam drawing