Even in a simple one-subject photo, there is information. There’s the hand, that can’t help but be there, in possession. 

There are the vertical stripes on that arse, that tell the expert eye that Arethusa was getting the cane, recently, while giving head for her Master. 

There’s the fact that the stripes aren’t very hard, that indicate that she was really very good at giving head. 

“Yes,” said Holmes. “Apart from the obvious facts that the girl has superior fellatio skills, is sexually submissive, left-handed, likes red rather than white wine, and frequently gasps when she sits down, I can tell you nothing whatsoever about her.”