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The easiest-to-navigate source of non-copyrighted images are the NOAA, NASA, US Forest Service, Bureau of Land Management & National Park service photo streams on Flickr:
https://www.flickr.com/photospeople/noaaphotolib/
https://www.flickr.com/photospeople/nasacommons/
https://www.flickr.com/people/usforestservice/
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https://www.flickr.com/people/nationalparkservice/
https://www.flickr.com/people/departmentofenergy/
NASA photos are typically in the public domain, while photos from other agencies are typically governed by the "Attribution 2.0 Generic" license which requires giving appropriate credit to the agency that produced them. Check the license for each photo.
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- Public domain
- No known copyright restrictions restrictions
- United States government work
can be used freely. Photos denoted with:
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"Young Monk Seal" is an Attribution 2.0 license image which can be used freely by crediting NOAA:
Photo credit: NOAA
"Jupiter's Great Red Spot as Viewed by Voyager 1" is a public domain image from NASA:
"Changing Arctic Ecosystem" is a United States government work image from the Department of Energy:
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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