This gets posted a lot, but it is in fact a photo shop job. If you look, you can see that there was another microphone hanging down to get one of the speakers in the cab. It's a microphone setup the engineer keeps permanently setup, usually for use with full stacks where the mic hanging down gets the bottom cab, and the 421 up top there gets the top cab.
I can't remember the engineer who this belongs to, but he does in fact know more about recording guitars than almost any three people who post on this board.
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"Cowards can never be moral."
M.K. Gandhi