Finding an image like that is an extremely long shot, almost like hitting the moon from your back yard with a rock.
Abraham Lincoln didn't sign Confederate oaths of allegiance. You may also wish to check the date on this man's release from prison -- it almost certainly dates from some time after Lincoln's death.
After the failure to capture Fort Stedman (March 25, 1865), little time remained to record all the casualties before the fall of Petersburg. Rather than run the gaunlet back to their own lines, many Confederates involved in the assault remained behind and were captured and sent to prison.
Here's a web page that includes several links specific to the attempt to capture and hold Fort Stedman --