as mac said if you didnt copyright the content then theres nothing you can do
if they copied the content and it was copyrighted, then you can formally ask them to take the content down, and if they fail you take the matter up with attorneys/lawyers in the country that you host from or your home country, if you host in the USA you get the advantage of using the DMCA copyright laws to your advantage and they are required to take the content down and.
i warn you that it would get expensive very quickly if you have to involve lawyers so you need to weigh up whether content has that high a value to you (eg does the content make you money that you are now losing with the copyright infringement)
also depending on the content they copied and how they are doing it, you can sometimes preventing making further copies and if they are just hotlinking your images you can setup some hotlink protection that doesnt display the image on there end but an image you specify (and this image could shame them publically on there own site)
