Of course it's not real. How can you even ask that question?
It's not even a matter of seeing the join or the difference in skin tone.
Just ask yourself - would he really do this? How often does a major sports star at the height of his career pose for hardcore nude photos? What exactly is the likelihood of this happening? It's not like it's a tastefully suggestive modelling shoot for a calendar or a commercial, such as your Beckhams or Frenchies might do. It's flat out pornography.
It's like the fakes of Prince Harry that people swear up and down are real. I mean - really? Are you that gullible? Getting caught by the paparazzi having a piss behind a tree is one thing. Posing for a naked photoshoot when you're a member of the fucking Royal Family is quite another.
(and yes, I know there was that rugby guy who did erect photos for FamousMales, but he's the exception that proves the rule, and he regretted it.)
Also, Ben Cohen is British, and therefore more likely than not to be uncut.