Hmmm, he looks Burnside-esque, but Burnside was lacking hair on top even at an early age. That photo portrays Lt. Col. Thomas D. Chamberlain of Maine, one of those who "stood firm" on Little Round Top the afternoon of July 2, 1863.
Edit - Although C. Thomas Howell played Tom Chamberlain in the movie, I have to interpret your answer as saying this is a picture of C. Thomas Howell - and it isn't.