Our own sad story. A few months ago, the Dear Rich Staff modified (perhaps 'transformed' would be a better verb) a clip art image and used it at our blog. A few weeks later, we got a letter from a lawyer representing the clip art owner demanding a bunch of money (at least enough to buy a couple of kayaks) or face a lawsuit. Fortunately, we made enough noise about fair use to keep the lawyers away (although of course, the statute of limitations hasn't run on that one). But the message is clear -- don't assume that clip art is free to use or modify.
Understanding the Terminology. The terms clip art, public domain art, royalty-free art, and copyright-free art are often used interchangeably (and confusingly). So here's a primer:
Clip art is a general term used to refer to any artwork that is available in a collection, either in a book or on a computer disk. Clip art may be in the public domain or royalty-free.
Public domain art is not protected by copyright. Many publishers, such as Dover Books, specialize in offering collections of public domain art. You are free to copy and use the individual artwork in a public domain collection without permission. However, you are not free to copy and sell the collection.
Royalty-free art is protected under copyright law and cannot be used for free. However, once you buy the CD-ROM or pay for access to a website that contains royalty-free artwork, your license to use the images is largely unlimited, so you can usually use the works numerous times for a broad range of uses. Use for merchandising -- putting the image on a t-shirt -- or some commercial endorsements -- using the image in a magazine ad -- may not be allowed -- a major exception to the rule that you can use royalty-free images any way you like.
Copyright-free art is the most confusing terminology. Some people use it to refer to public domain artwork; others use it to refer to royalty-free artwork. Often, it's used to describe artwork that websites offer for free to the public -- whether the works are public domain works or royalty-free works. We think it's a meaningless term.
Creative Commons artwork.To be on the safe side, clip art users might want to consider filtering their image search by using the Creative Commons image search filter (that's how we found "Sad Cat" by Peter M., above). And check the license to see if it fits your purposes.