Agree, the landscape really doesn't match and apart from erosion there's just no other explanation for the vast differences in the background.
I have also read up into the whole facial recognition side of things and it seems that very few experts hold much faith in it. A good example would be the British Metropolitan Police, following the 2011 riots, the police could only match one face out of 4000 (cctv footage) using the software, the problem is that CCTV footage is normally low quality so what chance the software has with an old tintype is anyone's guess. So, that really only leaves the location which is not really a match. As you have already pointed out, some documentary evidence is needed which places those people in a specific location at a specific time and that just doesn't look like that will ever happen. So there you have it, I'm converted, a disappointed convert but a convert non the less, I'm not going to give up hope though, I just hope that one day someone will turn up with an authentic photo of Billy. What an elusive character he was, I'd like one day to be able to say that I visited the grave of Billy but it seems even that's a tall order, two graves both claiming to belong to Billy, sigh, I'm going to have to visit both. Oh well, at least I didn't part with millions of Dollars for a 'tintype', I can't remember where I read it 'probably in True West Magazine' someone posed the question 'if you had millions of dollars to spend on an authentic artefact of the old west, would you spend it on the tintype croquet picture?' I'd have to say.....No.