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Some of the photos claim to be governed by the "Attribution 2.0 Generic" license which requires giving appropriate credit to the agency that produced them, while NASA photos are typically in the public domain. Editor's note: I strongly suspect that the Attribution 2.0 generic photos are also in the public domain, but the Flickr pages state otherwise.Make sure to check the license for each photo. Some photos are provided by private citizens as a courtesy to a government agency. For example, this landscape is copyrighted by Natalie Bell, even though it is included the US Forest Service's photo gallery.
There are absolutely stunning images in these galleries.
"Theodore Roosevelt National Park" public domain image from the National Park Service:
"Young Monk Seal" which can be used freely by crediting NOAA for the image:
Photo credit: NOAA
"Jupiter's Great Red Spot as Viewed by Voyager 1" public domain image from NASA:
The second-most easy-to-use database of royalty-free images is Wikimedia Commons. It has over 72 million images and many of them are in the public domain and can be used for any purpose.
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