For those new to art history (and for general inspiration for everyone) discipline-specific guides to art research and writing about art can be very useful:
Writing a research paper means documenting, or "citing," the sources of the information you use. How do you cite your sources? Every time you quote from or mention another person's writing or research in your own paper, you also mention the source of that work in a little aside called an "annotation." At the end of your paper, you include a list called a bibliography of all the sources you used throughout.
There are many different ways to annotate or call out sources in your paper, and many different ways to format the bibliography. These are called citation styles, and the professor who assigns a paper (or the publisher of a paper if it is being written for publication) tells writers which style they should use for any particular paper. Two common styles used when writing about the arts are Chicago (the Chicago Manual of Style) and MLA (the MLA Handbook).
Here is a short, authoritative guide to image citation from Colgate University:
Rogier van der Weyden, Saint Catherine of Alexandria. 1430-1432, Diptych panel, 18.5 x 12 cm. Kunsthistorisches Museum, Vienna, Austria. Available from: ARTstor, http://www.artstor.org (accessed September 30. 2009).
Caravaggio, The Denial of Saint Peter. Early 15th century. Oil on canvas, 94 x 125.4 cm. The Metropolitan Museum of Art, New York. From: The Metropolitan Museum of Art, http://www.metmuseum.org (accessed September 29, 2009).
Friedrich von Schmidt, Vienna Rathaus. 1872-1883. Source: Harshil Shah, Vienna - Rathaus. 2009, Digital Image. Available from: Flickr, http://www.flickr.com/photos/harshilshah/3823135957 (accessed September 14, 2012).
The Robert E. Hemenway Writing Center at the the University of Kentucky offers free and friendly help to all UK students, faculty, and staff. Graduate student consultants and undergraduate consultants assist with the process of composing and communicating in writing, speaking, and multimedia projects across the curriculum, at every stage of the composing and communicating process.
The Writing Center is located in the W. T. Young Library Hub in room B108B.