If you use canva (http://www.canva.com), you can access free images through its search bar. Then you can use Lunapic’s editor (https://www140.lunapic.com/editor/) to make dozens of changes. I’ve used these two tools together to create most of my images and graphics.
Thanks for all the suggestions! I’m adding this thread to my “favorites” so I can find it when I need a source.