A project of NASA and the Internet Archive. From the About page:
NASA Images is a service of Internet Archive ( www.archive.org ), a non-profit library, to offer public access to NASA's images, videos and audio collections. NASA Images is constantly growing with the addition of current media from NASA as well as newly digitized media from the archives of the NASA Centers.
The goal of NASA Images is to increase our understanding of the earth, our solar system and the universe beyond in order to benefit humanity.
The NASA imagery offered on NASAIMAGES.ORG is generally not copyrighted. You may use this NASA imagery for educational or informational purposes, including photo collections, textbooks, public exhibits and Internet Web pages (personal or otherwise). This general permission does not extend to any use of the NASA insignia logo (the blue "meatball" insignia), the retired NASA logotype (the red "worm" logo) and the NASA seal (the "NASA Properties") whether or not used in conjunction with images obtained from NASAIMAGES.ORG. Notwithstanding the foregoing restriction, you may use the NASA name and the NASA initials only as indicators of the original source of the NASA imagery.
If the NASA images obtained from NASAIMAGES.ORG are used for commercial purposes (including advertisements or packaging), such use may not suggest, either explicitly or implicitly, that NASA endorses any commercial goods or services.
Downloading and using images from NASAIMAGES.ORG does not grant you any ownership right in the image(s) and you must not claim rights in the images.
Since neither NASA nor the Archive requires a written model release for each image that has identifiable people in it, we cannot guarantee that you will be able to use such images for any purpose you like. Therefore, if a NASA image obtained from NASAIMAGES.ORG includes an identifiable person, use of the image for commercial or other purposes may infringe that person's right of privacy or publicity, and permission should be obtained from the person depicted in the image.