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If you spend a few minutes browsing, you can see that there are absolutely stunning images in these galleries that are in the public domain or that can be used freely with attribution.
"Theodore Roosevelt National Park" is a public domain image from the National Park Service:
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"Jupiter's Great Red Spot as Viewed by Voyager 1" is a public domain no known copyrights image from NASA:
"Changing Arctic Ecosystem" is a United States government work image from the Department of Energy:
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