Thanks for the prompt reply to my query. I hadn't thought about comparing it to a Springfield photo, but I'll do that. Brady, of course, is the most famous of the Civil War photographers, but this photo was taken bay a Brady partner, then competitor (actually by members of Alexander Gardner's team, namely Timothy O'Sullivan and -- whoops! I'll have to look up the name of the other gent, I've got it somewhere).
You're certainly correct about battlefield photographers using "props" and having a supply of such. Of course, around Gettysburg a few days after the battle there would be a supply of discards one would imagine. Not all the bodies were discoverd -- let alone "covered" -- until many days after the battle. Devil's Den especially thick with the slain. And the woods nearby.