I know this a old post. But that is not Billy the kid. Close, but the angle of the ears on the found photo are not even close.
The new found photo, the angle of the ears has a very distinctive sharp angle running from top to bottom inward.. In the first found one the ears are clearly more rounded. No it is not the hat changing them either.The hat is not even touching the ears in the known photo. And even if it was, that would not change the downward angle of them..
Now the guy on the left, his ears are shaped like Billys in the original photo.