The supposed spirit would appear as a faint impression of their earthy shape, sometimes in the background, sometimes touching the living person in the photo. The most well-known of these spirit photographers was William H. Mumler. He discovered the process of double exposure by accident, believing at first that he had captured the image of a ghost. Once Mumler figured out what had happened, he saw the market value of producing these kinds of images for sale as “proof” of spirits among us. The reason he is well-known is because his fraud was revealed when he created a double exposure of P.T. Barnum with Abraham Lincoln in the background and Barnum was called in to testify against him in the court case. Despite Barnum’s testimony, Mumler was acquitted, though his professional prospects took a nosedive after the trial.
Even though Mumler’s spirit photography had been called into question, many people still believed that the dead could show their energy in photos. Harry Houdini set out to disprove this possibility and also attacked the mediums who held these fraudulent seances. One of his targets in the 1920s was the medium, Mina Crandon. Houdini even so far as to reproduce her tricks on stage in a humorous manner. The great losses during World War I and then the Spanish Flu epidemic meant that hosts of mourners were looking for some sign of their loved ones. Mediums, spiritualists, and photographers filled a niche market for those looking for connections to the dead and spirit photography had a brief resurgence.
While we now know that these images were created using double exposure photography, there are still those who believe that these images might show another side of life and death. Certainly at the time they were produced many people believed that they were witnessing the photographic essence of spirits.
If you thought this was interesting, read about the ghost story which was used as courtroom testimony in the 1890s right here.