Thinking this over, I think Mr Clay is right. First of all, I don't buy the zip line thingumujic, just as I don;t buy most of the Miranda and her elusive "source's" spy reports, which I think are nothing more than informed speculation at best, and fanwanking at worst.
I don't think we will see the origin of The Joker. He will have his white face - and it can be make up, who knows (personally, I think it is - apart from the scarring round the mouth, I think The Joker wears white make-up on his face, and shoddily applied red lipstick round his mouth) - and his "Bermejo smile" from the get go. It seems that he is wearing a clown mask just like the rest of the goons. They don't have to put Ledger in full-Joker make-up while filming most of his scenes with the clown mask, so that can account for the set photos where he does not sport the actual Joker look.
The most probable scenario is that there is a bank robbery; it goes slightly awry, the Joker kills the bank manager, and, either before or after the shooting, takes off his mask to reveal his face. That second photo when he is staring down at the camera might be a scene where he looks down at the bank manager, but that's conjecture.
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