Here is my take on the picture, Yes I'd say both men are Veterans of Gettsgurg and my guess is the man on the left is Union and the man sitting on the rocks is Confederate. Photographers of the Gettsyburg reunions often ask a Reb and Yank to pose together for a photo. Also there looks to be two men in the background probably veterans. From the clothes the two men have on (turn of the century) I would say we are looking at a picture from the Fiftieth Anniversary of the 1913 Gettysburg Reunion.