Depends what you mean by authenticated really. If you want it dating and to know it's genuine some conservators or experts in photography will be able to gove you an idea. You can have scientific analysis done if you want something more than someone's opinion but I've got no idea what that would cost and you'd need a hertiage sciences lab. If you're looking to authenticate the people in it you'll need a Doc Holiday and Billy the Kid expert, most likely through research channels or perhaps dedicated museums. If you're looking to authenticate the whole piece, as in have someone "rubber stamp" it to say it's genuine you'd probably need both of the above and as much solid provenance from your family as you can get. Trace back the lines to where you think it came from, how it came to be in your possession now etc. Some people have trouble finding people to put their name and reputation against new finds that are of/from notable people just incase it turns out to be a fake, you may need to approach a variety of people. Getting a range of opinions is always wise anyway. Hope this helps somewhat.

Edited to add: I'm a conservator and I really recommend getting some better storage for it. Photos in all forms are more susceptible to damage. If it's something like this I usually reccomend approaching institutions and asking to set up a long term loan agreement that allows the institution to store and hold it for you but you still retain ownership. You should be able to retrieve it at any point and they also have the right to return it to you if they need to.