Took some screenshots of models in my viewer.
Thought there is sth on my monitor at first:
Nope. It is in the image.
I remember reading about that kind of stuff long time ago. Maybe just fragments from the TGA to JPEG algorithm.
Or is that to find out who leaked WoW alpha images to the press? That would make sense at least. I would watermark my images in alpha state aswell.
*edit*
Tested it. Information is not included in TGA screenshots and JPG screenshots at quality 10. All other screenshots include that kind of fragments. Fragments seem to differ depending on chosen quality.