The NASA website hosts a large number of images from the Soviet/Russian space agency, and other non-American space agencies. These are not necessarily in the public domain.
The SOHO (ESA & NASA) joint project implies that all materials created by its probe are copyrighted and require permission for commercial non-educational use. [2]
Explorer 6 (also known as Explorer S2) Photo (to replace wrong one in Wikipedia article of same) NASA photo http://space.skyrocket.de/doc_sdat/explorer_s2.htm
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