Although the artist is unknown, the portrait was initially thought to be of Emperor Franz Joseph of Austria (1830-1916).
For more about him see Franz Joseph I of Austria - Wikipedia, the free encyclopedia 1165
However, from the comments below, left by kind visitors, it is now suspected to be King Albert of Saxony (1828-1902) who reigned from 1873-1902 and is shown here in several different images.
Albert, was born April 23, 1828. Prince Albert's education, as usual with German princes, concentrated to a great extent on military matters, but he attended lectures at the University of Bonn.
King Albert was noted for his military ability. At the age of 21, he served as a captain in the army of the duchies of Schleswig and Holstein in their war against the Danes.
In 1866, during the Seven Weeks' War between Austria and Prussia, Albert commanded a Saxon corps, which distinguished itself at the decisive Battle of Königgrätz by a firm stand against the Prussia
Although even then, it is conceded the man in the miniature does not seem to have enough medals, and it is probable many officers of the time adopted a similar appearance!