NatGeo had a special on tonight about authenticating a photo that was purported to be of Billy. They went to great lengths matching terrain to the photo.

One problem: The photo was flipped.

[firsttoknow.com]

There's woman on a horse at the far right. She's sidesaddle. Sidesaddles can only be mounted from the left, and the skirt falls to the left. Since it falls to the right, the photo must be flipped.

And I had an 1880s sidesaddle (stolen, sadly, at a horse show), a Western one, that had a single horn and was only meant to be mounted from the left. So yes, I do know what I'm talking about.