Artstor Images for Academic Publishing (IAP): Free images for use in academic publishing, provided by museum collections.
CC Search: Search across several repositories, including YouTube, Google, SoundCloud, and more, for still images, music, and videos.
Flickr: Creative Commons: A collection of images published on Flickr using a Creative Commons license.
Getty Open Content Images: Search over 10,000 images from Getty Museum and Research Institute collections made available for download.
JSTOR Open Community Collections: A collection of open archival images, postcards, archaeological materials, and documents from several archival collections hosted by JSTOR.
NY Public Library Digital Gallery: Open access to over 700,000 digital images from the new York Public Library's collections.
Public Domain Project: Thousands of audio, image, and video files in the public domain from the collection of the Pond5 stock footage company.
Shared Shelf Commons: An open-access database of image collections shared by institutional users of Shared Shelf.
Smithsonian Open Access: An open access collection of over 2.8 million (and counting) high-resolution two- and three-dimensional images from across the collections of the Smithsonian.
U.S. Government Photos and Images: A vast collection of photos and images from the U.S. Government, many of which are in the public domain and free to use.
Wellcome Images: Providing access to the visual collections of the Wellcome Library, which documents "2000 years of human culture" with a focus on biomedical imagery. Most images are open access, with others available for paid licensing.