Yes, that's right. I feel totally pissed now. Why? Look at this: [link]
(edit: yes, no image in there at the moment. Read down a little further)

Now, guess what?
click here

These people STOLE MY image. They didn't credit the artist, they didn't link back, they just took the download link from deviantart and inserted it in there. I'd have been fine if they had at least asked me, but nothing as that.

Now, any opinions what I should do? I've never dealt with copyright issues, so a little advice would be nice. Thanks in advance.

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Update
As these people are obviously trying to ignore me (I sent them two emails, on 5/18 & 5/31), I'm gonna take measurement #1: disable the download possibility. If they're gonna trying to evade by using a different link, measurement #2 will follow: I already prepared a nice and huge watermark which will cover like 80% of the entire picture. This should take care of them. Hopefully. Buttheads.
At this point, I want to thank everyone who has helped me not going totally crazy and taking the (in my opinion) best and easiest way
All for now. Cheers