The sites below offer excellent images for research in art and art history and are especially good for illustrating a research paper or creating a class presentation. See the Web Resources tab for many other resources.
American Memory Project
Bridgeman Art Library
Visual Arts Data Service (VADS) -- A well-designed site with focus on fashion, craft, 2D design, and contemporary artists working in the UK and internationally. Repository for many specail collections in the UK.
Web Gallery of Art
Cybermuse
Digital Image Library, University of Oxford -- This web site offers central access to digital collections of Oxford libraries.
The Visual Resources Association--a professional association of image managers--has released a Statement on the Fair Use of Images for Teaching, Research, and Study. This document decribes guidelines for students and faculty wanting to use images in a research setting.
http://www.vraweb.org/organization/pdf/VRAFairUseGuidelinesFinal.pdf