If the pictures are properly credited and they're not being sold, I don't see how it falls under the category of theft; they're just displaying them without permission. Call the paper and tell them you want the pictures taken down. If you enjoy the company of lawyers, you should probably consult one. Here in the U.S., it's highly likely that all you'd wind up with is a legal bill and a bad taste in your mouth. Unless the copyright is registered with the U.S. Patent Office, all you're entitled to are actual damages, (no legal fees or punitive damages) and if the offending publication doesn't ordinarily pay a fee for such displays, it's a lousy bet that there will be any damages to collect that are worth the hassle. If this is the worst thing that happens to you, consider yourself lucky. Anything you post online is going to be copied and used by somebody, somewhere. If you're putting high-quality images on the internet, it's like leaving your wallet on a park bench and expecting it to be there when you get back.