I have learned more since I discovered this old photograph. My Grandfather and my Great-Aunt Barbara Hasselbacher both had a copy of this postcard. On one, the man identified by the arrow was called "Barbara's Father's Brother." That would make him the half-brother of my Great Grandfather Johann Hasselbacher. I know exactly where he fits now.
In his civil birth record, a son was born in Diespeck to Johann Konrad and Margaretha Hasselbacher on 14 Feb 1892 and named Georg. On Georg's son's marriage record in 1939, he signs his full name as Leonhard Georg but was known as simply Georg.
Amazingly, while searching for something else, a person saw this photo on my website and recognized the location. (He sent a photo, shown below, of one of the buildings in the background.) It was taken in Würzburg at the Sedan Kaserne (Sedan Barracks) in Ysenburg Street. (The coincidences continue.) During WWI, it was from this barracks that soldiers went to the battles of Sedan and Verdun. Before WWI, the Barracks were where the Ulanen were stationed. These were the mounted Calvary that would have fought in the Franco-Prussian War of 1870. Following that war, my Great-Grandfather Johann served in the Ulanen. In WWII the post remained a military base, and I would not be surprised if it was also used by the Americans after the war. Eventually it became a school for the police. Coincidentally again, after the war Leonhard George Hasselbacher became a policeman in Würzburg. Georg married Maria Halley and had a child, Joesph. Joseph was captured on the Russian front and died in a Siberian gulag in the 1950's. Joseph was the last of that line.
Someday I hope to visit the Barracks to see if I can recreate the photo and find other traces of Georg's life.