Yes, your picture is what Mary would have shot, I think you got it just right. So, the question now is what was so damning in Mary's photo that they had to pull a switch?
You're right, that is the big question, and I don't claim to be the best judge of it. I would just be guessing. But, it had to be very big, very damaging. Just think: they stormed her house that night at midnight to get the photo back. They couldn't wait until the next morning? They had to wake her up? They already had copies and a negative, so why did they need it at all? It must have been a real eye-opener- something that gave it all away.