Copyright does not prevent your work from being copied

Copyright is mainly about commerce.

As most artists know, copyright goes into effect the moment your work is "published. " This means the moment it is made public, the moment you show it to someone else, perhaps even the moment it is finished. You do not have to register the copyright, although doing so gives you certain legal advantages should you ever have to sue someone for infringement.

But a copyright does not keep your work from being copied except in the sense that it is a reminder to people not to do it. It is merely a ticket to a courtroom. In reality, you'll probably never even get to a courtroom unless you already have a record that your work is commercially valuable. Basically, you'll have to show not only that the work you are suing about is actually your own original work, that you made it before the alleged copy was made, that whomever you are suing copied your work on purpose, that it was close enough a copy that art collectors or other potential buyers would confuse it with your work and the copying could reasonably be expected to impinge upon you income or had or would hurt you financially. In addition, if the person you are accusing has no financial assets that you could get hold of if you won, no lawyer would take the case (unless you wanted to pay an hourly rate just to pursue it). You could hire a lawyer (perhaps at a reduced rate through your local Lawyers for the Arts) to write a cease-and-desist sort of letter to the miscreant, though.

There are other, more creative and probably more effective, ways to deal with copying, however. For instance: If someone has put an image of yours on their site, that may be a good thing -- if you can turn it into that. Contact that person and thank them for liking your work so much that they wanted to use it. Be polite and not sarcastic. But explain that, because of fairness and copyright law, your work can only be used with explicit permission from you and that you give them that permission if -- and only if -- they give you credit for the image and provide a direct clickable link to your site. Since they already have a favorable view of you work, your goal is to make them in effect an "agent" for it.

All of that assumes that you don't mind having your work publicized on that site. If the site is incompatible with your values or aesthetic or anything else, you will probably want to ask them to take it down. There are creative yet perfectly legal ways of dealing with this but I don't have room here.

One very useful thing you can do to deal with potential copiers: put a "use license" notice on your site, probably as a link. It could say something like, "All the material in this site is copyrighted but you can license any of the images for specific use. You must contact us first and pay a use fee. Fees start at $xx." Now if you find a commercial site has copied your work, you can contact them and explain your terms and bill them for the fee. You'll probably also want credit. They may or may not agree immediately, but always keep in mind that your goal should not be to stop this awful thing that has happened but to turn it to your advantage.