What about stock photos? There is a license CC0 that allows content creators to use pictures for FREE. Some photographers might require photography credit, or if there are people in the photo, a release form may be necessary. I include a few sites that offer stock photos; however, make sure you always check for user requirements and type of copyright. Check out PEXELS, pixabay, 500px, StockSnap, Kaboompics, Magdeleine, Freerange, UNSPLASH, Freeimages, and Gratisography.