In the context of publishing, "public domain" means works that for a variety of reasons are not protected by copyright and so are free for public consumption. Art enters the public domain in several ways. Two of the most common are:
I. A work is declared by its creator to be in the public domain
These are works--often images or computer software--that are declared copyright-free for any use whatsoever without restriction, even for profit. No attribution needed.
II. A work passes into the public domain after its term of copyright expires
Many images are protected by copyright, the same as textual works, for a set period of time. For information on when art images would customarily fall out of copyright and enter the public domain, visit Cornell University's Copyright Term and the Public Domain in the United States.
Art work "published" (made available for public viewing) before 1923 is generally now in the public domain. Even digital reproductions of these works (though the reproducers may claim copyright on their reproductions) can be considered in the public domain to the extent that the reproduction is true to the original and cannot claim any originality. This would be particularly true of photographs of paintings, or digital renderings thereof.
Some significant challenges will likely arise in determining the public domain status of a work:
a) Photographs of scupture or architecture, where the photographer could claim originality in the photo itself, may still be copyrighted if the photograph was published after 1923. Library staff can provide you with more information on this. Only an attorney can offer legal advice, however.
b) Some works created prior to 1923 were never published (made available for public viewing) until recently. These could include, for example, photographs from a private collection never released to the general public prior to digitization. Further investigation with the owning institution may be needed to determine when the images were first "published" for copyright purposes.
The term "nonexclusive license" applies to work licensed for open use by the copyright owner. Unlike public-domain works, these works are still under copyright, but the owner has licensed them explicitly for use by the public at large, most often for non-commercial use without the need to ask permission or pay licensing fees, so long as attribution is given. Commercial use of these images may entail asking permission or paying fees.
Creative Commons images
Gateway to photos and graphic art licensed for varied use. In general, no permission is needed. Always give attribution. Licienses vary, so read each license carefully.
Flickr Creative Commons
Searchable site of contemporary photos licensed specifically for varied use. In general, no permission is needed. Give attribution. Licenses vary, so read each license carefully.
Directory and searchable site of contemporary stock photos. Generally no permission is needed. Give attribution. Licenses vary, so read each license carefully.
Penn State Free Media Library
A gateway to free media from a variety of sources.
Over 70 million freely usable media files.
Books, magazines, or newspapers published prior to 1923
Images from books published prior to 1923 can generally be digitized and shared without asking permission of the copyright owner. You can photograph images from older books in Trexer Library or in your personal library. Many such books have also been digitized through online book projects like Google Books (http://books.google.com). As a courtesy, it is best to always provide attribution.
Library of Congress Digital Collections (http://www.loc.gov/library/libarch-digital.html )
Massive collection. Any materials in this collection initially published prior to 1923 should be available for use without permission, as they have passed into the public domain. Use with caution, as publication dates vary, and this can be difficult to determine, especially if the images come from a private, previously unpublished collection. Look carefully at the metadata for each image: the Library of Congress typically provides ample information about rights and reproduction. Consult with a librarian for additional guidance. Use for not-for-profit purposes only, such as student multimedia projects or educational conferences. Always attribute.
NYPL Digital Gallery (http://digitalcollections.nypl.org/)
New York Public Library's collection of historical images--photos, drawing, paintings--can be used for noncommercial purposes without restriction so long as the images were originally published (as opposed to created) prior to 1923. Look carefully at the metadata for each image to see if an image was published prior to being digitized, and if so, when. Credit should be given to the NYPL as a courtesy. Consult with a librarian for additional guidance.
Old Book Illustrations.com (http://www.oldbookillustrations.com/)
Digitized illustrations from books in the public domain. Unrestricted access and use, whether commercial or noncommercial.
I. Consider if the statute of fair use will cover you.
It is likely that if your use is educational, limited to the classroom, and you're not duplicating a work, but are pointing to it, or you are securing a duplication of the work at a password-restricted website like Blackboard or the library's electronic reserve system, that you will be protected by fair use and will not need to seek permission from the copyright owner.
On the other hand, if you are using the work in a more public venue, such as posting the work to the open web or using it in your own publications, then the claim for fair use is substantially weakened.
II. Request permission from the hosting website or copyright owner.
The source website or copyright owner may agree to your use, sometimes charging a fee, sometimes not.
For tips on citing print and electronic sources, visit Trexler Library's Citation Guides for Print and Electronic Resources.
Or visit the Online Writing Lab at Purdue.
For automated citation, try the shareware Zotero.
For help with annotated bibliographies, visit Purdue's Online Writing Lab for definitions and format of an annotation.