In the old days of photography, when every picture looked like its own illegal low-rez download, you couldn't take one without some weird smudge or shadow invading the frame. So of course, it didn't take long for people to start claiming that those smudges were in fact ghosts and/or other supernatural beasties photobombing you. Before long, spirit photography became the trend du jour of the late 19th century, though the reason was a bit more depressing than, say, why the selfie stick caught on. After the Civil War, there were plenty of grieving Americans wanting something to remember their fallen loved ones by. Spirit photography promised to connect the bereaved living to the probably annoyed dead in return for nothing except the satisfaction of knowing that they'd helped to cure someone's emotional pain ... and lots of money.
National Media Museum via The New Yorker
The most famous of these scam artists was amateur photographer William Mumler. In the 1860s, visitors to his studio often found themselves sharing the shot with a long-dead relative dropping in. Over time, he grew more infamous, somehow managing to survive several attempts by skeptics to debunk his photographs. At the height of his career, even Mary Todd Lincoln dropped by to see if she could have a picture with her husband, bringing Abraham Lincoln back for one last encore -- the irony of which was clearly lost on the poor grieving woman.
Lincoln Financial Foundation via Smithsonian