[Tom Edgerton]

Put simply, you can't use someone else's source material without their permission. Under copyright law, it's illegal. This use can be negotiated, of course, but most times expect to pay a fee. They may also require a credit line, as in your case. And get any agreement in writing, in advance. If you try to negotiate this after the fact, the photographer or artist can ask for anything they want, or prevent you from using it.

Also by law, you must get permission to reproduce someone's image from the person themself or their agents--not just permission from the person who took their picture. This doesn't just apply to celebrities or public figures, it applies to anyone. And it doesn't matter if they're gone. Elvis may be dead, but Lisa Marie and Priscilla are very much alive and so are their lawyers.

If you are in the portrait business, you must know the law. If you circumvent it, and are found out, you are exposing yourself to major lawsuits and heavy fines that could put you out of business. Don't expect to hide it by working "under the radar." It's a small world, especially if you post your work on the web.

Be professional. And be smart. Nobody will accept "I didn't know."