This picture came out a couple of years ago on Ebay and caused quite a debate in the Lincoln historical community. Someone did a computer analysis on it and determined that this was NOT Lincoln. I remember it well, because a couple of my colleagues and I had a very intense discussion about it at the time.
I remember when this photo first came to light, or at least articles were first being published about it. As I recall, it was never 100 percent proven that it was Lincoln. Personally, I doubt that it is.
I remember that auction. I did not believe it was him then, and I do not believe it now.
In addition, the head of the younger man in the daguerrotype appears smaller in comparison to the body.
I'm not aware of Lincoln's relatives, specifically if he had any brothers. I've never heard of any.
It's certainly within the realm of possibility that the man in the daguerrotype was a Lincoln relative, but it's just not Lincoln himself.
Is there any documentation that the daguerrotype was produced in or around Springfield, Illinois, where Lincoln was living and working at the time? I would tend to doubt it.