I recently bought the book - "1001 photographs you must see before you die", the history relates to each photograph is very interesting.
In1860s, William Mumler used the double exposure technique to combine two images together. He was very active during the American Civil War period when million people has been killed, for revealing the dead in the same image in his portrait business. It is called Spirit Photography. He was later on trail for his "fraud". A busy man in the dark room.
