I thought like Void that it had to do with showing faces in stock photos because you have no release of permission from the person in the photo. Perhaps there's a different reason, though.
See when I asked for clarification, one mod told me it was alright as long as it was us, and it was not posted on the forum, since chat rolls off. Then one mod told me it was not ok at all. So I just have aired on the side of caution and just do not post my face.