d is for double exposure. when i was a photography student at asu, one of my favorite things to do was shoot double exposures. sometimes i would shoot an entire roll of film, rewind it and shoot it again. other times i would re-shoot each frame. it was fun to shoot this way with my digital camera. i can set my camera to shoot multiple exposures in each "frame" - up to 5. i just shot 2 per frame and didn't look at any of my images until i "developed" them lightroom. other than adjusting the tone a little bit, i left them unedited as well.