18. A system for tracking a user, comprising: a processor; and a memory communicatively coupled to the processor when the system is operational, the memory bearing processor-executable instructions that, when executed on the processor, cause the system to at least: receive a depth image; identify an estimated location or position of a part of the user in the depth image; adjust a model of the user based on the estimated location or position of the part of the user; and in response to a failure to identify a location or position of the part of the user in a second depth image, associate the part of the user with a portion of the second depth image based on a location or position of a default position of the part of the user.
20. The system of claim 18 , wherein the memory further bears processor-executable instructions that, when executed on the processor, cause the system to at least: provide the model to a gesture library.