Gaa!
Because leaving the copyright on an image you modify for your bands use is the same as getting permission from the original artist.... Arg!

Yeah,... there's the novelty of randomly discovering that someone appreciated my/your/somebody's work to use it in a positive context, but they really should have at least approached you and asked. A quick e-mail wouldn't have been hard. As it stands, not only has this Engine reproduced a protected image without consent but they modified it to boot, and their modifications do not alter the original to make itself its own, separate work.

It's kinda like a pedestrian walking down the street, seeing a car, and liking it so much that they hop in, drive it off, and get it detailed, but they never take the license plate off. Of course, that'd be carjacking and there are laws against that, too.

Had you image been released to the public domain, everything would be different. You chose to copyright the artwork; if I were you, I'd make the copyright do its work now. I don't mean instigating some crazy-ass legal battle or anything, but have them get official consent and add a credit/mention in their Myspace thingum, or have them remove it. With the copyright, you made the serious decision to protect what's yours.

It's still nice artwork. Oh, and yours is the most interesting spelling of your name I've come across.