
It helps a lot if you know the exact location of the photograph. It also helps if you know the date, although the stamp box on the backside of the postcard will help you determine that.
Real-photo postcards were developed on various papers, and they often included markings that help narrow down the date. For instance, this one has the letters AZO and 4 triangles pointing up. Because of this, we know that the postcard was printed between 1904 and 1918. Not exact, but better than nothing!
Here's another one, with an Al Capone look-alike on the right.

The letters PMO indicate that the picture was developed between 1907 and 1915. That's, of course, very disappointing to me, because Al Capone was born in 1899, so that would make him no more than 16 years old in this picture. So, I guess it's probably not Al. Darn! Well, at least you can see the usefulness of these stamp boxes for determining the date. If you would like more information, Playle's website provides an easy guide to determine the dates of old cards.
Today is Sepia Saturday, so click on the link to view some beautiful sepia photographs accompanied by colorful stories.