Writing history or historical fiction takes research if you want to get it right. These photos are among the sorts of things I’d put on my wall or computer screen if I were writing about WWI.
I always look for images to help build the places in my imagination. One of my favorite sources is the Library of Congress. LOC photo collections are fabulous. Check them out after you look at these.
These Unseen Photos From World War I Are Unbelievable
http://io9.com/these-unseen-photos-from-world-war-i-are-unbelievable-1580681616
sharon p. lynn 
I don’t know why I never thought about using the Library of Congress for historical pictures. It’s so obvious. I think I’m used to just Googling it and hoping for the best. Thanks so much for the advice!