Wikimedia Commons contains over 27 million freely usable media files, including images, sounds, and videos. The highest quality items are ‘Featured’ by the site and appear in picture of the day and picture of the year selections.
Europeana is an archive of millions of digitized items from European cultural heritage institutions. Multiple formats (image, video, text, sound) are available. Please read licences of images as they vary.
Flickr Commons is a repository for historical images from cultural heritage institutions such as libraries, museums, and archives. Most material has “no known copyright restrictions” and is free for noncommercial use. Please check licences.
All images require attribution, and are licenced under various levels of Creative Commons licensing unless licensing is not listed on an image which means you should contact the journal. Collection is from The Open Access Subset of PubMed Central (PMC), a free full-text archive of biomedical and life sciences journal literature at the U.S. National Library of Medicine, the Indiana University hospital network, the Orthopaedic Surgical Anatomy Teaching, and the Collection at the USC Digital Library.
Smithsonian Open Access lets you download, share, and reuse millions of the Smithsonian’s images—right now, without asking. With new platforms and tools, you have easier access to nearly 3 million 2D and 3D digital items from the Smithsonian collections This includes images and data from across the Smithsonian’s 19 museums, nine research centers, libraries, archives, and the National Zoo.