That's a good thought Ron. I am running off memory here but I have a book titled "Portraits of Conflict A Photographic History of Louisiana in the Civil War" by Carl Moneyhon and Bobby Roberts. It's been a while since I've read it but I believe they mention that many soldiers were photographed with their Bibles. Again, just running off memory here but I have read that somewhere. If not in that book then somewhere else. That is what influenced my guess.

I want to get the book they did for Mississippi as well one day. If you aren't familiar with these books then check out this page...

http://www.uark.edu/~uaprinfo/titles/backlist/history/poc.html

If that is a signal corp operations manual that would make this particular photo very unique. In either case it's a great picture!