Increasingly, museums provide access to major portions of their collections online and are therefore rich sources of images. It is also worth remembering that some – the Met, the Louvre, the National Gallery (U.S. and U.K.), the Tate, the British Museum, and many others – are rich sources of information on provenance, exhibition history, artist biography, and bibliography as well.
Some museums, such as the Getty, allow their images to be freely used; while this is a growing trend, most museums require permission and sometimes a fee to use their images and most impose limitations on how their images may be used. Be sure to check museum websites for Rights and Reproductions information on copyright and how to cite their collections in addition to copyright and citation information found here or elsewhere.
British Library Digitization Labs
A vast quantity of digital images have been made available for research purposes online and within the British Library. The collections are truly diverse, encompassing prints, drawings, maps, art works and photographs, as well as illuminated manuscripts, digitised bookbindings and philatelic collections. Click this link for a selection of collections available for research purposes.
Gallica (Bibliotheque Nationale)
One of the most important digital libraries available for free via the internet, Gallica provides access to printed documents, including French books, newspapers, and magazines from the 17th to the 20th century, manuscripts, sound and other media, and archival documents, maps, and plans. Includes many images from (for example) illustrated books and journals, archival documents, and manuscripts.
Library of Congress Prints and Photographs Online Catalog
Contains catalog records and digital images representing a rich cross-section of still pictures held by the Prints & Photographs Division and, in some cases, other units of the Library of Congress. The collections of the Prints & Photographs Division include photographs, fine and popular prints and drawings, posters, and architectural and engineering drawings. While international in scope, the collections are particularly rich in materials produced in, or documenting the history of, the United States and the lives, interests and achievements of the American people.
Metropolitan Museum of Art Digital Collections
The Met's digital collections include Met publications from 1869 - 1974, rare books from the library's collections, items on bookbinding and book collecting, texts, images, and fashion plates from the Costume Institute, Japanese illustrated books, Knoedler & Co. exhibition catalogs and Macbeth Gallery exhibition catalogs, rare manuscripts, rare books published in Imperial and early Soviet Russia, trade catalogs from the 18th century to the present, and much more.
New York Public Library Digital Gallery
provides free and open access to over 800,000 images digitized from the The New York Public Library’s vast collections, including illuminated manuscripts, historical maps, vintage posters, rare prints, photographs and more.
Yale University Digital Collections
The cross-collection search retrieves results from over 500,000 images in selected Library Digital Collections. These collections include the Yale Visual Resources Collection, Beinecke Rare Book and Manuscript Library Digital Images Online and the Yale Department of Classics Collection.