1. For use by a computing system including one or more processors that are running first software instructions, a method for extracting user behavior from a depth image that includes a plurality of pixels that correspond to a user that is interacting with the application running on the one or more processors, 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 provide input to second software instructions running on the one or more processors, wherein the second software instructions may comprise the first software instructions, wherein the input to the second software instructions running on the one or more processors comprises at least one of the following: a command or action to control or activate a user interface element of the second software instructions; a command or action to animate an avatar that is being displayed under control of the second software instructions; an update to a position or movement of an avatar, character or other on-screen object or image that is being displayed under control of the second software instructions; or an update to tracking of the user performing an exercise or pose so that feedback or points can be provided by the application to the user.