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https://www.flickr.com/people/nationalparkservice/
Some NASA photos are typically in the public domain, while some of the photos from other agencies 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. Make sure to check the license for each photo. Some Certain 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.
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"Theodore Roosevelt National Park" is a public domain image from the National Park Service:
"Young Monk Seal" is an Attribution 2.0 license image which can be used freely by crediting NOAA for the image:
Photo credit: NOAA
"Jupiter's Great Red Spot as Viewed by Voyager 1" is a public domain image from NASA:
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