Yeah it would prove it. No scammer, with the possibility that the forum pool is going to find out the username of the criminal (bitcoins paid to the scam have been traced the this forum's hardware buying pool, if you can believe it), would post their picture under that username, thus proving they are the criminal. All the FBI would have to do is trace the I.P. address of that member, then go find the face that used it.
You're operating under the assumption that they are guilty and that they need to prove their innocence. If I were them and I just got scammed, I would say "fuck you" to this idiotic demand.
Prove they are guilty, and then we'll talk. Until then, STFU.