I watched the program and I would have a hard time convincing myself to drop $5M on this picture (assuming I had that kind of jack). All the evidence was very circumstantial and there was no clear provenance (i.e. chain of possession) for the item.
I'm not saying this Tintype is worth $5M or that it will bring anywhere near that amount. Supposedly there are two interested buyers negotiating to buy it. One of those buyers is very likely to be William Koch who owns the only other authenticated Tintype of Billy the Kid ($2.3M). I hope the two Tintypes can be brought together for the first time ever in a private collection. As a collection their individual values will increase & sometime down the road Koch (or his estate) will be rewarded for his investment, as it should be. In the meantime the Tintypes will be preserved & well cared for.
As far as the authentication process, the building & the location, the identification thru other Tintypes of most everyone present that day, the diary, etc were more than enough to convince me. At this point in time all evidence of authentication can only be circumstantial and there can be no provenance in support of a lost Tintype photo.