Mrs. Tinkman and "ghost" by William H. Mumler (American, 1832 - 1884), taken c. 1862 - 1875; Albumen silver. Spirit photography was believed to capture images of ghosts and other spiritual entities. It was especially popular in the 19th century, first used by William H. Mumler in the 1860s. He 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 (mostly using other photographs as basis). Mumler's fraud was discovered after he put identifiable living Boston residents in the photos as spirits; however, the practice was adopted by other photographers and remained popular through the second half of the 19th century.