GRIN is Great Images in NASA. The library of images of air and space exploration can be copied and used freely without seeking permission from NASA. You can investigate the heart of the Crab Nebula and enjoy the space fireworks observed from the Hubble Telescope. There are 93 separate categories of GRIN images. You can determine the resolution of the images that you download. It is an astounding free, high-quality gift.
http:grin.hq.nasa.gov
