I'm an instructor in the Armed forces, as such I often find myself teaching with PowerPoint, and have started a habit of browsing /wg/ and using wallpapers to get away from the bland, aesthetically mindless designs provided by my command.

help make my classes more visually pleasing to my soldiers?

I'll dump wallpapers I've used in the past as examples, I try to stay away from guns/modern military type (unless I'm displaying a specific weapon) images and follow themes:

-Map/compass/wanderer themes for navigation
-landscapes for camouflage and concealment
-science/mechanical themes for weapon systems and equipment
-winter landscapes for cold weather training.
-Medical themes for combat first aid and triage. et cetera

anything philosophy/motivation is decent too, I leave them as a slideshow on breaks...
help a dude out?