Once it was enlarged I could tell that the pins had the initials "S. My hunch was that he might have been a member of the Salvation Army.Checking out various web sites on the Salvation Army and comparing pictures of Salvation Army members for sale on ebay helped me identify the photo and my ancestor.We've all heard terms like Cartes de Visite, Cabinet Cards, and Daguerreotypes.
Costume In articles about dating photographs one of the ways to identify them, which is emphasized time and time again, is by looking at your ancestor's costume (or clothing).
Photos taken during the Civil War may have a tax revenue stamp on it.
Jewelry might help date a photo especially in cases where men are wearing fraternal organization medals.
Likewise, The Costumer's Manifesto at drawings and pictures from different eras. If so you may be able to help date a photo by what photographer's props are visible.
Dover Publications has quite a few books on everything from clothing to hats to military uniforms. Details What details might help you date that family photo? Photography studios used painted backgrounds after 1840.