Image credit: (Copyright expired) archive image
Uploader comment: The first ghosts in photographs were the result of accidents. During a long exposure--such as those required in photography's infancy--a person who stood still would register as clearly as a building. But a person who moved out of camera range after only a portion of the exposure was completed would instead appear as a see-through blur.
Image status: HOAX Demonstrating how long exposures can produce "ghosts" in old photos.