It sounds like you are being scraped at a rate that you probably will never be able to keep on top of. Have you considered putting your actual artwork behind a password, and using the "public" portion of your site to entice people to come in (with text and watermarked thumbnails, for example)
The whole DMCA system fails where piracy is rampant, because it's reactive and not proactive. You will never get Google to *prevent* people from scraping your content and ranking for it unless you block it from Google altogether. So from a practical standpoint, unless you like spending your time this way, that may be the way to go.
(This may be a topic for the SEO forum as opposed to the AdSense forum, since it doesn't sound like it's AdSense publisher related)