This is a relative of John Koster in German uniform from the late 19th century. The printing on the back of the picture indicates that it was taken in the town of Güstrow which is in the same area where the Heidens and Rambows originated in Germany.

Heinrich Rambow (right) served in the Seven Weeks War (Austro-Prussian War) in 1866 and the Franco - Prussian War in 1870-71 prior to coming to America in 1874.  He probably wore a similar uniform.

A "Maler" is a painter.