I was quite surprised about the domain, since it’s Hungarian (wohoo!), but the quality is absolutely spot on. Searching for any term will yield pages of relevant stuff. The top line of photos is from their stock photos site for cash, but all the others are free and of the same quality. The most you will have to do is five acknowledgement or notify the author, which is the least I can do for a godo image.

You can also use Flickr and DeviantArt, but in this case you will have to ask for permission in advance and I’m an impatient guy, so I only do this if I really love an image. It isn’t nice, but in theory you can use any image you find on the web. Where do you get your free images, I’d love to get some more sources!