Comments? I think Imran has a point.
How about adding a column img_license to the image table and requiring the user to specify a license during upload:
That's precisely what the image's description page is for, and its already being used for that (or should be wherever it's not). The Wikipedia:Copyrights page is about as clear as I can make the muddy situation. Yes, included images may not be covered by the GFDL. We cannot accept /text/ that is not licensable under the GFDL, but images are different. They are easy to separate, denying ourselves "fair use" would be a great hardship, fair use wouuld apply to most of our licensees anyway (though not all), and using images does not detract from our goal of creating free text.
I think it /would/ be a mistake to use a non-free image that the article /depended/ on (say, a diagram). If there are any cases like that, I think we should replace it with our own image under GFDL. But images that are just illustrations to otherwise complete articles (like the album covers) are fine.