Copyright Friendly Images

With grateful thanks to Christy DeMeyer, Teacher-Librarian at Golden Senior High School for building this list :-)
NO Citations/Attribution Typically Required
Open Clip Art Library -
U.S. Government Photos - Vast majority are public domain but a few links direct you to sub-sites where you will see a disclaimer limiting use.
Pics4Learning -
PicDrome - (Public Domain pictures)
Flicker Commons - -
Alegri Photos-
Burning Well -
Public Domain Images -
Public Domain Pictures -
Google Stock Images - 5,000 stock images for use in your Docs, Sheets, and Slides. Go to Insert > Image, click on Search, filter to Stock photos, and search for the images that you want.
Free to Use with Credit/Attribution
Free Photo Gallery -
FreeFoto -
Creative Commons -
Wellcome images (medical & social images)
Wikimedia Commons -
Open Photo Project - (blocked)
Picture Collection Online (New York Public Library)

History Focus
Great Images in NASA (GRIN)
Images of American Political History
America From the Great Depression to World War II: FSA/OWI 1935-1945
American Memory Collection: Library of Congress--click on "Photos and Prints" and check the "Copyright and Restrictions" section for each collection
American Memory Maps Collection
Selected Civil War Photographs
USDA Historical Photos

Science Focus
NASA Image Exchange
NASA Multimedia Gallery
NASA Photo Archive
NASA's Planetary Photojournal
National Health Museum (AccessExcellence) - great images for science (biology, cell processes)
National Library of Medicine: Images from the History of Medicine
NOAA Photo Library (National Oceanic and Atmospheric Administration)
Public Health Image Gallery
Science Images
Science Images (Earth Zone)