NOAA Photo Library
From the NOAA website:
Educational use is encouraged as the primary goal of the NOAA Photo Library is to help all understand our oceans and atmosphere so as to be better stewards of our environment for future generations.
A few photos in the NOAA Photo Library that are known to have copyright restrictions are so noted in the caption information associated with those images.
Credit MUST be given to the National Oceanic and Atmospheric Administration/Department of Commerce. Where a photographer is noted, please credit the photographer and his/her affiliated organization as well.
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