**Remember, nothing on this page is legal advice to you.It is general information and may not apply to your circumstances. It also may not be up-to-date. Use it to learn the issues involved, not to make important decisions.**
So you think your image was stolen?
It isn't unusual to go to a POD forum and find a post screaming "Someone stole my design!" Well it does happen, and in many cases you can enforce your rights as the creator of the image. However, just as often the accuser is mistaken. The most common mistakes are:
The design was an affiliate site. The affiliate is simply displaying it to help you sell it.
The design is text only and not covered by copyright because it is too short.
The image has a common source or the source material is by its nature very similar.
Don't post links (or clues) to show everyone what you mean. If you need to provide evidence to follow-up privately email the POD's legal team.
Before you do that, investigate.
Is it an affiliate?
Go back to where you found the item. Copy and paste the address (URL) someplace, NotePad, Word, it doesn't matter. Click on it, and keep clicking until you get to the shopping cart. With each click copy the address so you have the complete path. Put the item in the shopping cart. It is important to be IN the cart, not the click before the cart.
Now the title of the item in the shopping cart should be a link. Click on it. Where does it go? If it goes to your store then no one is stealing from you. They are an affiliate helping to sell the PODs items, including yours. If it does NOT go to your store, copy that last link and then go to the next step of investigation. There are some PODs that may not require that link to your item. Just follow up if you aren't sure, ask, don't scream.
Your unique idea?
The bad news - no matter how unique, clever or funny you can't copyright an idea. You also can't copyright the short phrases that typically express those ideas on a t-shirt. The Copyright office doesn't have an exact definition of "short phrase" but pretty much if you can read it easily on a t-shirt it is likely too short to be protected by copyright.
You CAN trademark short phrases, but you'd know if you did that. So even if they take your exact words and use them, there is little you can do but fume. However, if you have artistic design elements THEN you might have something to protect, if they copied that expression, that art.
Great minds think alike
More bad news. It is really easy for more than one person to each come up with a totally "unique" phrase. Something seen or heard filters into the subconscious and pops out as an idea. Sometimes the other party really did "copy" and the law just isn't there to help. But the reason it isn't there to help is because the chances are very high that more than one person will come up with the same thing independently. It happens a lot. Person A accuses person B, who then presents really good evidence that they were actually first in time. Person A is red faced and humbled to learn the truth behind "Great minds think alike."
So ... if what you think was copied is "just text" you are probably not going to be able to do anything. There would be one exception. Let's say you proved it was not an affiliate, but the person has taken not just one phrase from you, but stuff from lots of people, and you can show it. Fine, gather the evidence, send it to the POD's legal team and let them investigate. Even if it isn't against the law rampant copying is bad for the POD and if it can really be shown that it is not coincidence they may decide to take action.
Is it a look-alike?
There are many times when two images look like one was copied from another but each are independent. It is to be expected that if you have hundred of thousands of visitors taking pictures of the same building or landmark that some of those pictures will be virtually indistinguishable. One photograph of the "White House" looks very much like another. Flowers, butterflies and common objects can all appear very similar. Roses look like roses, and monarch butterflies look like monarch butterflies. Yes, it is possible to infringe on these items but it is also very easy to make a mistake and believe there is infringement when there is none.
The same occurs with things like dogs in "show stack" - the whole point of a "show stack" is to put the dogs in virtually identical positions and the whole point of purebred dogs in the conformation ring is similarity of appearance. In these situations your "proof" of copying will need to be a lot stronger than if the image is more distinctive.
Even when people add their own efforts they can come up with extremely similar images. For example, if you are using clip art sometimes they just lend themselves to different people making the same changes.
Yes, it really is copied
OK, so you have done your investigation and you are honestly convinced that your work is both covered by copyright and was actually stolen. What next?
You could see if you can find contact information for the seller, contact them directly and ask them to take it down. If that doesn't work or you can't contact them or you just want official intervention then privately email the POD's legal team.
Before you do that decide how certain you are. To enforce your rights you have to sign a "demand" under penalty of perjury. If you sign that statement and you are wrong, you can be legally liable and that could get expensive. OK, so now do some research on the DMCA (Digital Millennium Copyright Act) - you will need to comply with those requirements in making your claim. And you make that claim by writing the legal team for the POD.
You can find examples here: http://www.plagiarismtoday.com/stock-letters/
Most PODs will comply with a DMCA notice and take down but they are not required to do so. A DMCA notice does not a require that the owner of the site take down the items you say are infringing. All a DMCA notice does is put the site owner on notice of the claimed infringement. If the site owner takes no action and you decide to enforce your rights through the courts then they will be unable to claim that they were completely unaware of the conflicting claims. PODs take items down because they deem that the benefit of keeping them is not high enough to justify the risks of legal expenses. Your contact with the POD helps them assess that risk. If you sound professional and educated about your rights you are a higher risk to the POD than someone who is blowing off steam and can't manage to meet the minimum requirements of a legal take down notice.
Finally, while you are not required to register your work to have a valid copyright you will be required to register before you can use the courts to enforce those rights. If you register after infringement you will only get actual damages. If you register before the infringement you can recover statutory damages and attorney fees. You don't need to register each individual image. You can register them as a collection.