Do you have a photo of your Civil War ancestor in uniform? If so, consider yourself very lucky. Photos of soldiers weren’t taken very often. When they were, they were taken on the soldier’s own time and paid for by themselves.
Many people hope to find a photo of their soldier, but unfortunately, there isn’t a collection of Civil War soldiers’ photos at the National Archives. The federal government didn’t ask for a photo of the soldiers and there was very little reason for them to need a photo in their records.
Occasionally you may find a photo in the soldier’s pension file, but even that is pretty rare. When photos do show up, they’re even less likely to be a photo of him in uniform. On the rare occasion that you do find a photos in a pension file, they’re likely to be a photo of him later in life.
In the rare times that a photo is included in a pension file, it's usually because some sort of investigation was being conducted. They have needed to verify that a soldier really did serve in the war, so they may have taken a photo and asked his fellow soldiers if they recognized him. Or maybe the soldier needed to verify an injury, so he would include a photo of his wounded area.
Photos of Civil War soldiers, if they were taken at all, may still be in the family’s collection or uploaded to online family trees. I also see them show up at Civil War collectors’ shows. Many local historical societies have photo collections, so you may find some of them show up there as well.
The site https://www.civilwarphotosleuth.com/ is doing some interesting work with facial recognition and Civil War photos. You may get lucky and find something from your family there too.