To add another post, this is an awesome picture. There are levels and levels of authenticity here.
The soldier is portraying one of Longstreet's soldiers in Cobb's Georgia Legion who made the long train ride from Virginia to Georgia just after Gettysburg. They arrived in Ringgold and started toward Chickamauga while listening to the cannon booming and arrived just as the battle was ending. They had just gotten resupplied in Richmond with shell jackets made of English wool that had a blue tint. This caused a little confusion I believe at the Battle of Wauhatchie (correct me if wrong). They would hang out with Bragg on Missionary Ridge before setting out towards Knoxville and took a hammering at Fort Saunders. They made it back to get hammered again in the Overland Campaign and Petersburg.
That rusty rifle though, for shame.