Even if an image is "free" it should still be acknowledged if you use it. A Harvard reference for an online image would look like this:
Norfolk, S. (2016) Oscar Niemeyer staircase [Online image]. Available from: <http://www.simonnorfolk.com/meanderings/meander-01>
You can find guidelines for referencing images and other sources on Skills for Learning.
A collection of approximately 40,000 images, plus over half a million links to other resources, from the Conway and Witt Libraries of the Courtauld Institute in London.
Archive from the Associated Press, containing more than 3,000 photos a day from journalists recording news as it happens around the world. For more than a century, AP has captured the greatest moments in history, breaking news, sports, politics and entertainment.
Artworks by British artists bought to demonstrate the very best in contemporary British practice in all medias. Over 8,500 works of British art can be found on the website.
The British Library has uploaded over one million public domain scans from 17th-19th century books to Flickr. The images are maps, geological diagrams, illustrations, comical satire, illuminated and decorative letters, illustrations, landscapes, wall-paintings and more scanned from 65,000 volumes held by the British Library and they can be used and adapted for any purpose.
More than 800,000 images from the British Museum’s Collections.
Online examples of pioneering design with images from the museum's collections.
Explore over 58 million digital resources, including artworks, artefacts, books, videos and sounds from across Europe’s leading galleries, libraries, archives and museums.
Getty Images is a photobank of stock images and photographs, made available for use in websites, blogs and social media platforms through their embed tool (only currently works when off-campus).
The J. Paul Getty Trust makes freely available all digital images to which it holds the rights, or that are in the public domain, to be used for any purpose. Currently, there are more than 140,000 images.
A large online photograph collection, including art, architecture, industrial design, and textures. All images can be downloaded and used freely with copyright restrictions.
This collection include photographs, fine and popular prints, drawings, posters, and architectural and engineering drawings. While international in scope, the focus is on materials produced in the US and content documenting its history. High-resolution images are available to download and the vast majority are copyright free.
A compilation of openly licensed image collections from several cultural institutions. All of those listed contain images that can be freely used without restriction.
The online image database of the RIBA British Architectural Library, the world's most extensive visual archive devoted to architecture. Includes photographs, drawings and engravings, covering world architecture of all periods together with related subjects such as landscape and design. You can browse the images or download them for educational purposes.
Over 783,000 images from the V&A collections.
The Library has a collection of film, television and video games available to borrow.
To search the collection go to Discover and on the Advanced Search screen choose which format you would like the results to be, e.g. DVD video, sound recording, etc.
A really useful collection of videos that you can use for local historical / contextual research. The Yorkshire Film Archive is a registered charity which finds, preserves and provides public access to moving image made in or about the Yorkshire and the North East of England.