I'm sure I've previously read about these sorts of people being employed by various intelligence agencies. Maybe it was just in some fiction novel, but it would

I'm sure I've previously read about these sorts of people being employed by various intelligence agencies. Maybe it was just in some fiction novel, but it would make a lot of sense. I think they were referred to as flashers. That is people who could be flashed a face, and remember if they'd seen it before. Very useful for going through mug shots to see if they had any known aliases associated with the same photo/face. Can anyone provide any more information?