Their site : http://35mmdoubles.blogspot.fr/
“Awesome female photographers Vanessa Morrow and Steph Parke combined their talents a couple years ago to create The Doubles Project. The two ladies take photos with 35 mm film and then send rolls to each other to shoot on top of, resulting in some truly stunning double exposures.” - http://designismine.blogspot.fr/2013/02/seeing-double.html