I agree with Imran that fair use materials in a GFDL document are a problem. In essence we tell our readers "we grant you the right to do what you want with these materials, just follow the GFDL", but we are in no position to make such an announcement: we don't own the copyright to the fair use materials nor have we received permission from the copyright holder. Our readers *cannot* do what they want with them.
Like Cunctator says, invariant sections don't provide a way out.
Short of dropping fair use materials altogether, we could clearly label the fair use status of images on the image description page, maybe even saying "This image is *not* under GFDL, it was copied from ... under the fair-use doctrine." And our [[Wikipedia:Copyrights]] should then contain a notice that for the license of images, the description page ought to be checked.
In essence, the image then becomes a separate document from the rest of the article, with a separate license. It may not be completely clean and is not very pretty, but I think it's the only thing we can do.
Axel
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