Object tracking techniques

Techniques for efficiently identifying objects of interest in an environment and, thereafter, tracking the location and/or orientation of those objects. As described below, a system may analyze images captured by a camera to identify objects that may be represented by the images. These objects may be identified in the images based on their size, color, and/or other physical attributes. After identifying these potential objects, the system may define a region around each object for further inspection. Thereafter, portions of a depth map of the environment corresponding to these regions may be analyzed to determine whether any of the objects identified from the images are "objects of interest"-or objects that the system has previously been instructed to track. These objects of interest may include portable projection surfaces, a user's hand, or any other physical object. The techniques identify these objects with reference to the respective depth signatures of these objects.