Metropolitan Museum Of Art (400,000 free online images for non-commercial use)
Library Of Congress - Items From the LOC's Collections - Free To Use and Reuse Sets Of Books, Newspapers, Manuscripts, Prints, Photos, Maps, Musical Scores, Films, Sound Recordings, and more.
Library Of Congress - Thousands Of Photos, Posters, and Images That Are Free to Use And Reuse
Library Of Congress - Free eBook Downloads
Creative Commons - Non-Profit That Hosts Work People Agree To Share With Others, "Copyright Free"; great resource for accessing and using a variety of work. The site even creates the attributions for you. Read about Creative Commons attributions here.
Creative Commons - samples of 2 billion works available. Click a sample photo to see how the image opens a Creative Commons page, complete with attributions you can copy and use for that image.
Pixabay - 2.8 million royalty free images, videos, audio, and other media; under Creative Commons
Flickr/ Creative Commons - browse through millions of media where others have chosen to share their work under Creative Commons license. Attributions are listed for you too.
Flickr Free Use Photos - Advanced Search - search by content types, license types, date taken, and date uploaded. Content includes photos, screenshots, illustration art, photography, and videos.
FlickrCC Blue Mountains - photos of the Blue Mountains in Australia, showcasing the beauty of the mountains including forests, waterfalls, mountains.
Flickr Library Of Congress - The Commons - features over 41,000 photos from the LOC's prints and photographs collections; released under Creative Commons license
Freepik - free graphics, icons, and illustrations; some under Creative Commons, but not all; be sure to check license terms
Free Photos And Images (All photos on the site are in the public domain)
Google Images - search for images on the WEB and add to slide presentations; must check for copyright licenses. Google Image Search does not just render copyright free images. Use the "Usage Rights" drop down in the "Tools Menu" to search by license and copyright information.
Google Images Advanced Search - filter image searches by words, phrases, file type, image size, color, type, region, usage rights, and more. Find images you are free to use or ones that have copyright restrictions. (Scroll to the bottom of the page and choose, "Usage Rights."
Gratisography - free high resolution photos; released under Creative Commons Zero. The site says, "Peace of mind license without copyright restrictions."
Pexels - free stock photos, royalty free images and videos; free to use; attribution not required; photos and videos can be modified
Pics4Learning (copyright free library for teachers & students); has curated image library that, "is safe and free for education. Teachers and students can use the copyright-friendly photos and illustrations for classroom projects, web sites, videos, portfolios, or any other projects in an educational setting."
Free-Images.com - free public domain photos, art, and vector images
PicFindr - Search Public Domain & Free Stock Photos
Designs For Democracy - 200 Years Of Drawings From The National Archives; an exhibition of nearly 124 design drawings selected from the vast holdings of the National Archives and Records Administration.
Digital Public Library of America - over 48,000,000 images, texts, videos, and sounds from across the United States. "DPLA is a U.S. project aimed at providing public access to digital holdings in order to create a large scale public, digital library."
National Park Service - find a national park by state; each national park has a collection of photos and a gallery of photos for visitors to use.
National Park Service - Historic Photo Collection
America As It Was - Collection of Post Cards
U.S. Department of Agriculture
U.S. Department of Interior - Photos
U.S. Department of Interior - Archived Photos
Library of Congress - American Memory
Federal Resources for Educational Excellence (Featured)
Federal Resources for Educational Excellence (All)
National Atlas.gov
NASA Image Exchange
National Library of Medicine
Public Domain Photos And Clip Art
Congressional Pictorial Directory
Congressional Pictorial Directory, Wikipedia
FreeFoto.com
Clip Art Images of World History
Public Domain Clip Art
Free Stock Photos and Images
Springfield Township High School Free Images
Free Photos Bank (free stock images)
Free Pixels (images for personal and commercial uses)
4 Free Photos
Public Domain Pictures
Public Domain Clip Art
Art Images
FreeMediaGoo
Free Military Photos
FreeFoto.com (largest collection of free photos on the WEB)
Images For Education
Photos For Class
Public Domain Pictures
Public Domain Images, miscellaneous images
Photos8
Reshot
Stockio
U.S. Government Photos and Multimedia
Free Digital Photos
Flickr Free Use Photos
Flickr Storm (use pull down menu for Flickr and Creative Commons - easier)
ClipArt ETC
Open Clip Art Library
Unsplash
U.S. Fish And Wildlife Services Images
U.S. History Images
U.S. Navy Images
Wikimedia Commons - Collection of 46 million usable media files to use for FREE