Thanks so much Scott for posting these. I can see differences but as you pointed out we have an opportunity to get an expert opinion. I will chip in half of the cost to pay for
Joelle Steele's opinion.
My inner-historian wants to contribute a little money to run the analysis to hopefully get a more definite answer, but....
...my inner-cheapskate doesn't think it's worth it to spend the money on this without any clear provenance which attempts to link the photo to the Lincolns or a written account by an eyewitness or a family of an eyewitness.
So with these too parts of this history buffy's heart in conflict, I guess I must turn to logic. Since this tintype is up for auction, I think it is more appropriate for the seller or auctioneer to pay for a relatively cheap verification test which could increase the item's sale value. So, historical curiosity in this instance has to give way to more practical concerns.
Thanks Scott, for your ear analysis and offer to get us in touch with this expert, even though I feel as though I shouldn't chip in on this particular instance.
While it would be interesting I, too, think it's not worth it. The seller is certainly too smart to do, but I'd recommend it to the willing-to-be-buyer (before buying...)