signifiers

"[T]he substance of a [digital] image, the matter of its identity, no longer has to do with paper or particles of silver or pictorial appearance or place of origin; instead it comprises of a pliable sequence of digital codes and electrical impulses.... It is their reproduction, consumption, flow and exchange, maintenance and disruption, that already constitute our culture."

Geoffrey Batchen, Each Wild Idea, 2001

sources:
http://www.neatorama.com/2007/01/02/13-photographs-that-changed-the-world/

http://www.worldsfamousphotos.com/