Google Advanced Image Search (Scroll all the way down to the bottom to "Usage Rights")
Other Ways to Locate Openly-Licensed Images
Creative Commons (Cultural Heritage) Search (beta) (Images only with an emphasis on openly licensed cultural heritage images)
CreativeCommons Search Search for openly licensed images in: Europeana, Flickr, Pixabay (public domain), Open Clip Art Library, and Wikimedia Commons. (Also includes options to find music & video)
Wikimedia Commons (Terms: CC and public domain)
Creative Commons Image Directories (Terms: CC and public domain)
The Noun Project (search CC-licensed and public domain icons by keyword)
Figshare (Terms: CC-BY Licensed) research-related images, data etc.
Compfight (Terms: CC and Commercial)
PhotosForClass (Creative Commons licensed images from Flickr -- required citation information is automagically added!!)
These are just a few of the many places to find openly-licensed images or illustrations.
Public Domain images
* Public Domain: Works whose exclusive intellectual property rights have expired, have been waived, forfeited, or are inapplicable.
Getty public domain content (Attribution required: "Digital image courtesy of the Getty's Open Content Program")
Library of Congress (click on "Rights and Restrictions")
Various public domain image websites (Terms: public domain, but read the fine print)
Attribution is ALWAYS REQUIRED when using works that have a Creative Commons license. Learn how to attribute CC-licensed works by following these best practices -- or use a browser plug in such as OpenAttribute to help you.
The most common forms of attribution include the three elements, two of which are hyperlinked:
(c) Author Name "Name of work [hyperlinked to where you found the work]" License [hyperlinked to license]
License terms on some sites (this one is from Flickr.com) may appear as Creative Commons icons or appear when a hyperlink is moused over.