ADA (Archive of Digital Art) - (formerly Database of Virtual Art)
Archive of over 8000 computer-generated and digitally generated images, dating back to the 1970s. Entries also include published literature and exhibitions for artists where relevant.
Art Resource
Searchable image database of over 1 million images of fine art from major museums in Europe and the US.
Art UK
The website aims to make images of all publicly owned art in the UK available, and already has more than 200,000 images from over 3000 collections. As well as straightforward searches, you can also search by region. As of early 2019, there is very good coverage of oil paintings. Works on paper are still being added and a start was made on sculpture this year.
BASE
Search engine that finds material in institutional repositories. Of several such search engines, BASE currently seems to be the one that finds most images.
British Printed Images to 1700
Thousands of prints and book illustrations from early modern Britain, in fully searchable form.
Courtauld Institute of Art: Conway Library.
Over one million images: photographs and cuttings of architecture, architectural drawings and publications, sculpture (approximately 10,000 sculptors are represented), ivories, seals, metalwork, manuscript illumination, stained glass, wall paintings, panel paintings and textiles.
Digital Library for the Decorative Arts and Material Culture
Images (and texts) focusing on early American decorative arts. Compiled by the University of Wisconsin.
Digital Public Library of America
Large collection of material from the United States. After running a search for your subject, use the Refine your search feature on the left-hand side of the page to filter results to just images.
Digital South Asia Library: images section
This collection of images is based on six collections. The American Institute of Indian Studies which includes over 125,000 photographs of sculpture, terracotta, painting, architecture and numismatics. The Government College of Arts and Crafts from the Museum of Contemporary Art (Chennai) is a collection of photographs dated from the mid-1800s. The Keagle Photograph Library, Hensley Photo Collection and Bond Photograph Library all contain World War II photographs taken by American service personnel. The Oriental and India Office Collections is currently being prepared for the database.
Europeana
Digital images of over 10 million objects from collections throughout the European Union, including art works, museum objects and books. These include items originating outside Europe, e.g. East Asian art. Images and descriptions are provided by the home institutions rather than Europeana itself, so quality varies. Descriptions are in the language of the contributing institution, though a translation tool is provided. Confusingly, this is separate from the menu of languages for the site as a whole. Europeana is divided into many collections, including art history.
Getty Open Content Program
Includes images from the J. Paul Getty Museum, the Getty Research Institute, plus many other images of art works from the sixteenth to nineteenth centuries. More images of material from the Getty are being constantly added, and at some point this will include images from the Getty Conservation Institute.
Google Arts and Culture
A partnership with many leading museums worldwide. Each museum makes a selection of images of their collection available online. Some also offer a virtual gallery and a single zoomable art-work at extremely high gigapixel resolution. There is some additional multimedia content.
Haltadefinizione
Relatively small collection of reproductions of European old master paintings, mostly Italian, in extremely high definition with easy zooming. Digital watermarks make the images unsuitable for Powerpoint, but useful for close examination of particular works.
Himalayan Art Resources
Over 60,000 images of art works, mainly religious, from Tibet, Nepal, Kashmir and adjacent regions. Includes painting, sculpture and textiles.
Image search engines
Library of Congress :photos, prints, drawings
Among many other digital collections hosted by the Library of Congress are:
RIBApix
Images of architecture and interior decoration.
VADS: Visual Arts Data Service
Over 100,000 images and a great advanced search feature.
Visual Collections: images of art, history and culture
Over 300,000 images from 50 collections of art, though some are only available for a fee. Divided into 5 sections: cartography, fine arts, architecture, photography and other.
Web Gallery of Art
Allows users to search European painting and sculpture from 1000-1850. The database has over 27.600 reproductions as of August 2011 and is continually updated. This database also features a mobile version.
Museums and galleries
All museums and galleries have some images of their artworks online. Many go further with databases containing high quality images and excellent descriptions. Here are just a few particularly good examples.
Social media
**Please note** Images here may be in breach of copyright. In addition, information about the images, such as artists' names, may be incomplete, misleading or sometimes just plain wrong.
Most artists, museums, galleries, and other art world figures and organisations, have accounts on photo-sharing sites. For instance, you can browse the Tate Gallery on Instagram and the Tate Gallery on Pinterest.
Wikimedia Commons
A good source of public domain and freely-licensed images under a variety of Creative Commons licenses. The normal cautions about dubious attributions and inaccurate content apply. Please be sure to read the relevant license to see how an image may be reused.
WikiArt
Easy to search and browse. Although the project is large and has just started, it will cover the history of art including contemporary works and artists and currently features over 58,600 historical and contemporary artworks.