1. A method for extracting user behavior from a depth image that includes a plurality of pixels that correspond to a user, the method comprising: identifying a pixel of the depth image that corresponds to an extremity of the user; identifying an extremity blob that comprises pixels of the depth image that correspond to the user and are within a specified distance of the pixel identified as corresponding to the extremity of the user; identifying an average position of the extremity blob by determining an average position of the pixels included in the extremity blob; and using the average position of the extremity blob to update an application.