Once the user outline("drape") settles, it is used to locate the user's head-Figure 3(a) shows the head location superimposed on the live video. All this is done at frame rate in software on a standard, low-end PC. The head location can then be used for further processing. For example, we detect the"yes" and"no" gestures(nodding and shaking the head) by looking for alternating horizontal or vertical patterns of coarse optical flow within the head box. Another use of the head position is to match head subimages with a stored set, taken while looking in different directions. This is used to drive a game of Tic- Tac-Toe, where the head direction controls the positioning of the user's X.