If you are creating a propaganda poster, make sure that you think about tone. Neither the book nor the film would advocate recruitment - both understand the true costs of war, so your poster should reflect that tome (probably means you need to think about irony and maybe sarcasm (here' the difference: the root word for irony means "to dissemble," while sarcasm's root words mean to "tear flesh"). Goya's drawings (especially his titles) create the right tone. You can take a look at some posters here (you can see German and French posters from WWI (might be worth looking at those to see what visuals they use). You are welcome to create a poster that reflects the ones you see, but your poster's tone should be consistent with the tone in both novel and film.
I have attached a few of Goya's drawings. You can find more here and here. Pat attention to the titles.