1. A method for using a depth image to extract user behavior, comprising: receiving a depth image that specifies that a plurality of pixels correspond to a user, wherein the depth image is obtained using a capture device located a distance from the user, wherein the depth image also specifies, for each of the pixels corresponding to the user, a pixel location and a pixel depth, and wherein the pixel depth, specified for each of the pixels corresponding to the user, is indicative of a distance between the capture device and a portion of the user represented by the pixel; determining, for each of the pixels corresponding to the user, a pixel mass that accounts for a distance between the portion of the user represented by the pixel and the capture device used to obtain the depth image; and determining, based on the pixel mass determined for each of the pixels corresponding to the user, a depth-based center-of-mass position for the plurality of pixels corresponding to the user that accounts for distances between the portions of the user represented by the pixels and the capture device used to obtain the depth image.