"I imagine that the essential gesture of the photographer is to surprise something or someone, and that this gesture is therefore perfect when it is performed unbeknownst to the subject being photographed.  From this gesture derive all photographs whose principle is 'shock'; for the photographic 'shock' consists less in traumatizing than in revealing what was so well hidden that the actor himself was unaware or unconscious of it."

--Roland Barthes,
  Reflections on Photography