They're free to use, free to distribute, for both personal and commercial uses! They're 300dpi A4 size, so they're good for large/high-res images. I can't vouch for how good they are for printing, but from what I've seen they aren't half bad on paper. Credit is optional, but always appreciated. <3
Not for re-sale, because you can seriously just render something like this easily in Photoshop. I'm posting these for those who couldn't be bothered to make their own.
The ZIP contains more files than what are shown; there are duplicates with more contrast or inverted and have more texture. c: