Creative Commons Image Collections - Where graphics in the public domain can be found online, openly licensed, and used by anyone, thanks to the CC Search tool.
Flick Commons - A collection of images from cooperating cultural institutions worldwide that are in the public domain or otherwise unrestricted by copyright.
Flickr Creative Commons - You may browse or search through content under each kind of license on Flickr.
Wikimedia Commons - Public domain and freely licensed instructional media resources (pictures, sounds, and video clips) on Wikimedia Commons in their native language.
Pixabay - Licensed under Creative Commons CC0 - Can be used without providing credit for the artist.