I was pretty serious. How effective the DMCA request will be is kind of a question mark. You may want to look into it. If you send it to eBay, they may take down their listing right away. You may have to send it to the actual seller, who could easily ignore the request. I have only dealt with the issue once. I posted a really rare item on eBay and someone stole my exact picture at the same time of my listing (and undercut my price). Because their item had bids, eBay wouldn't permit them to alter the images in the listing. Instead, I took new pictures to solve the issue. It was annoying though.
Because you aren't really going to sue them, the request is merely puffing, unless you can send it to eBay.
Edit: here is a quick google that pulled up this tutorial. The DMCA takedown seems pretty easy (and free alternative)
No idea how legally correct that info is, but thought it would help since you this is a fight in principle that would be worth it to me.