Nice concept. I swapped a PDF on Pi-Calculus against a photoshopped Sumo wrestling match and "The Logic of ARIZ" against a photo of a very wrinkly old man. Personally, my interest would be sustained for longer if it were a bit more specialized, like if you could blind-swap technical/scientific papers, or short-stories. I'm not so much the photo guy, and this site apperars to be somewhat pic-biased.
