This is very interesting, and I also would like to see how this turns out. I ran across this sort of thing, back in 2004 or so. Had a friend with a very large military site. Was a guy in California who went around stealing content, from every military site on the web. He was able to do this by having many emails...(I think he had over a thousand) and a ton of fake names.
The only way back then was my friend posted his website and a warning in big orange letters on the bottom of every page. All of us who had links also advertised the warning. As far as I know this fellow is still online. I'm unaware if anything was ever done to this fella, but word sure got around.
He did a lot of sneaky stuff, befriend us then stole our stuff.
Like Lisa suggested, I think the only way these days is to submit a request to the IP of the offending person and have them deal with it. It's a sad fact, that a lot of people on the net can't come up with their own content or at least have the decency to ask to use it.
As a side note, I use a lot of mixed content, both mine and others. I keep good files, am always polite and always ask for permission. You would be surprised how many sites actually give me permission, then thank me for asking permission first. It always surprises me, that someone figures it's easier to steal from someone, then send a quick one or two sentence email, asking or permission.
Keep us posted.