The crowds that swarm through the streets and tourist attractions of London serve for some people, oddly, as a sort of screen. Everyone around here, they think, is too busy, too preoccupied, to take any notice of me. So they may withdraw from the throng for a while -- perhaps to daydream or connect with a friend nearby or just take a rest, enjoying a private moment in a very public space. London Off Guard records one photographer’s attempts to bring those moments from behind the screen into the light.