C1860s William M Gregg Tintype Photo Civil War Colonel 179th New York Infantry

  
Thanks for looking at this amazing piece of history. This is the only photo known to exist in the public of him.

No authentication on if this is him etc. I have included the two other known photos in the world side by side to compare, my opinion and a couple other specialists' opinions it does appear to be him. It also very much lines up as you can see on the tintype his various medals/ribbons from the war.