Unknown Confederate Lt. Colonel at actual size

Enlarged to 400%

Portrait at 1200%

Reverse at 300%.
The tax stamp tells us the photo was taken between August 1864 and August 1866. One possible reason for the photo: It might have been taken after the war of a former Confederate colonel who visited Baltimore. For the photo he put on his old uniform so he'd have at least one photo of himself in uniform. Any other possibilites?