30 October Warmup

Mary Todd Lincoln with a ghostly image of Abraham Lincoln
William H. Mumler

William H. Mumler was a SPIRIT PHOTOGRAPHER. He would take pictures of people and mysteriously the image of a long-lost loved one would appear in the photo. No one knew how Mumler did it, but today we would be able to do this fairly easily. Why do you think these kinds of images were popular in the early years of photography?