Spirit photography is a type of photography whose primary attempt is to capture images of ghosts and other spiritual entities, especially in ghost hunting. It was first used by William H. Mumler in the 1860s. Mumler discovered the technique by accident, after he discovered a second person in a photograph he took of himself, which he found was actually a double exposure. Seeing there was a market for it, Mumler started working as a medium, taking people's pictures and doctoring the negatives to add lost loved ones into them (mostly using other photographs as basis). Mumler's fraud was discovered after he put identifiable living Boston residents in the photos as spirits.