Since its creation in 1958, NASA has been taking pictures of the Earth, the Moon, the planets, and other astronomical objects inside and outside our Solar System. Under United States copyright law, works created by the U.S. federal government or its agencies cannot be copyrighted. (This does not apply to works created by state or local governments.) Therefore, the NASA pictures are legally in the public domain.
Photographs and other NASA images should include the NASA image number if you have it, for easy reference.
When accessing space photographs, be sure that you know the source. Pictures not produced by NASA employees may have different usage restrictions.