Multiple Exposure

http://www.petapixel.com/2012/09/28/people-vs-places-double-exposures-by-two-photographers-on-one-roll-of-film/

http://www.petapixel.com/2012/07/23/multiple-exposure-portraits-created-in-camera-using-a-dslr/

http://www.petapixel.com/2012/09/10/create-beautiful-surreal-photographs-by-stacking-your-film-negatives/

http://shuttermade.com/alisonscarpulla