The Smithsonian has this and says it is a real photo postcard.

Unfortunately there isn't any identifying information there. However, the entry at Wikipedia for real photo postcards indicates that Federal legislation didn't permit messages on the back of a postcard until 1907. Also, a Smithsonian article on postcards says this about the legislation:

>These changes to the backs of postcards ushered in the Divided Back Period, which spans from 1907 until 1915. The Divided Back Period is also known as the “Golden Age of Postcards,” due to the vast popularity of postcards during this time period.

This postcard has a message area on the back so I think the date is probably closer to 1910 than 1900.

From a Smithsonian Magazine article on black cowboys:

>The cattle drives ended by the turn of the century. Railroads became a more prominent mode of transportation in the West, barbed wire was invented, and Native Americans were relegated to reservations, all of which decreased the need for cowboys on ranches. This left many cowboys, particularly African-Americans who could not easily purchase land, in a time of rough transition.

Given the date of the photo the man might not have been a real cowboy but instead a man in a cowboy costume. For reference here is a post of a known black cowboy.