Who can sign off passport photos
Terminal thread drift here (sorry!), but I think the connection between those on F3G's list is that they are listed in directories that someone working at the passport office can readily check (in principle, I'm sure it happens very rarely). Of course, that doesn't explain why (e.g.) CORGI registered gas fitters don't appear there.
PS I'm with GBS: "Every profession is a conspiracy against the laity."