This picture, circa 1853, may be the first photobomb. Just look at that person in the upper left-hand corner, ruining a perfectly good shot:
As improbable as it sounds, there's a chance it really was the first photobomb (though the term "photobomb" itself, defined as the prank of popping up in someone else's photo, is firmly part of the 21st century).
The photograph's creator, Mary Dillwyn, was one of the earliest Welsh photographers in the 1840s and 1850s, and there aren't many other preserved photos that old. In addition, her informal photos were relatively unique for the time — using a smaller camera with a relatively short exposure time, she was able to capture fleeting expressions while other cameras could take more than a minute. So it's entirely possible that someone could slide into her picture as a practical joke, the same way we do today. At the very least, someone was sneaking into the frame.
The picture is a highlight of more than 4,500 images the National Library of Wales recently released into Wikimedia Commons. And you can browse a gallery of Dillwyn's photos here, including other charmingly natural photos, as well as what's probably the first snowman ever to appear on camera. But the photobomb may be the highlight: It's proof that people always loved ruining photos — even before most people knew what "photos" were.