I recently compiled a pack of around 2,400 free high-res Creative Commons NASA photos for artists to use in their work, you can check it out and download it below. I plan on putting more together as well, for free of course, so keep an eye out. Just make sure you read the usage info in the pack if you decide to use them. There's a torrent file available as well.
I'm also offering up over 1,250 images of my own personal stock from Australia for super duper cheap at $6 as a way to help me offset the cost of my time in putting together the free resource packs. Check it out if that interests you at all. If not, no worries, but you can enjoy and use these free examples from the Australia pack
Hope you find the downloads useful and get some use out of them, take care!