Just in case your opposing view fellow give you a hard time, I did in fact, find a full copy of the book online showing the picture. Go to google and type in --- photographic history of the civil war the opening battles Click on the first entry that comes up and put in page 105 in the appropriate box.
It is curious however, that Germaine M. Reed's "David French Boyd: Founder of Louisiana State University" (LSU Press,1977) does not include that photograph in her publication. Her book does show nice pictures of Boyd though as a faculty member before the war at the Louisiana State Seminary of Learning and Military Academy in Pineville and in Confederate uniform. As for Venable, that is the only photograph that I know that exists of him.