You´re not the only one who can see those stripes. However a promotion to Corporal isn´t shown in the muster rolls.
KELSEY , CHAUNCEY.—Age , 44 years. Enlisted, August 29, 1862, at Morris, to serve three years; mustered in as private, Co. C. October 14, 1862; killed in action, October 28, 1864, at Boydton Plank Road, Va.
Lieutenant Charles H. Dygert, who commanded the regiment (!) mentions Private Chauncey Kelsey and his death (musket ball) in this report.
Not that it helps, but my gg-uncle mustered in as a sergeant and out as a captain. However I see him on official rolls after the war as anything and everything in between -- Sgt., 2nd. Lt., 1st. Lt., Capt.
IMHO, the photographer (for such an elegant studio setting) or a friend probably loaned him the jacket for the picture. They all just figured he eventually would be promoted to corporal.
I believe that GELonstreet's post would most likely confirm he was not a corporal when the picture was taken.
Chauncey Kelsey appears in the U.S. Census of 1850 with a wife, Jane, and three children -- Sarah (11), James (7), and Martha (6). Five years later, in the New York state census (above), his wife is listed as Ann J. [Jane?] Kelsey, and the three children are still there.