The supplement mentions this about backside texturing:

``` Texturing the back of the body is more difficult, as we have no direct observation of it. One approach is to sim- ply mirror the front texture onto the back. This mirrored- texturing produces reasonable results in some cases (e.g., arms), but undesirable results in others (face appears on the back of the head). To address this problem, we allow the user to choose between mirrored texturing or label-driven texture synthesis – “texture-by-numbers” – on a part-by- part basis. ```

[1] https://grail.cs.washington.edu/projects/wakeup/files/photo-...