Know your source. Know the terms of usage for each image you plan to use.
"Normally, the use of clip art images in ads, brochures, and newsletters is covered in the license agreement. However, some companies do impose certain limits. ...the resale of images incorporated onto greeting cards, t-shirts, and mugs...is normally not part of the standard terms of usage. However, some companies will sell additional licensing that allows the use of their images on resale products. — Using Clip Art on Resale Products
"If a work is within the public domain, it means that work may be used, modified or republished by any person, without the need for royalties or fear of copyright infringement." — Public Domain Clip Art - About.com Clip Art
Even if the images you want to use are provided free for commercial use, that might not include use on resale products. Carefully read the terms of usage provided with any free images obtained from the Internet. Track down the original creator of the image if necessary. Sometimes simply asking permission is all that's required. Other vendors or artists may require the purchase of additional licensing, just as they do for some purchased artwork.
Is It Really Free? Before You Use Any Image On Resale ProductsFor any use of images found online, especially commercial use, do your research to determine if the images are truly free. There are many sites out there that say they are distributing free images but are simply grabbing the clip art and photos from any number of places without determining if the author intended them to be freely distributed. If the site provides a name and link to the creator or photographer, locate their site online. Look for their licensing information.
If the creator or photographer is not named or is listed as unknown or if the same images show up on many different sites listed as free or public domain or with different artists listed, be wary. The images may not be truly free and you risk copyright infringement charges, especially if you use the images commercially — including on items for resale.
Free images are still covered by a copyright. It may have very liberal terms of usage but it is up to you, the user, to determine if the use you propose is within those terms of usage.
- Avoid Copyright Infringement: If it's not explicitly spelled out, ask.
- A Few Facts About Public Domain Clip Art: Just because a site calls it public domain doesn't mean it is.
- Avoiding Copyright Issues By Making a Few Changes: The 20% rule? Not a way around copyright.
- Creative Commons: "A Creative Commons license falls somewhere between the extremes of most copyright law: either "All Rights Reserved" (where all uses of the work are regulated) or "No Rights Reserved" (public domain works)."
Play it safe. Find out exactly what the license contains for any image you want to use on products for resale. If not spelled out, contact the creator or vendor and ask.