On the wikien list I had written:
By the way, this sentence contains at least one common misconception about copyleft. Images only "become GFDL" if they are released by their copyright holder under the GFDL. They don't automatically become released under the GFDL.
Someone replied the following (privately, so I'm not sure if ey wants eir name divulged):
Well, there is one more case: If the copyright-holder mixes his own images with GFDL contents, the result, if distributed, should become GFDL, because of the "viral" (or "cascade") effect.
Now that I realize it was a private message I begin to suspect even more that the person was simply being sarcastic, but since I wasted my time writing a reply here it is:
No, that is specifically what I'm saying is *not* true (maybe you were being sarcastic in which case I apologize).
If a copyright holder "mixes his own images with GFDL contents", i.e. prepares a derivative work derived from GFDL content and his own images, and does not release the derivative work under the GFDL, then that copyright holder has committed copyright infringement (barring a defense such as fair use, at least). The work is not *automatically* released under the GFDL.
Like I said, a work can only be released under the GFDL if the author intentionally grants a license. If they don't grant such a license, then there may be an instance of copyright infringement, but there is no automatic release under the GFDL. In this regard it is the same as the GPL.
I just looked for a good description of this in Wikipedia, but I really can't find one. Maybe I didn't look hard enough, but Wikipedia could really use some improvement in this regard. I was looking for a detailed description complete with citations from prominent experts and advocates on different ends of the spectrum (Eben Moglen, RMS, Bill Gates, etc.). Anyway, the best I could find was in http://en.wikipedia.org/wiki/Copyleft, under "Is copyleft "viral"?": "Second, even when the included code is substantial enough to warrant copyright protection, the remaining code will never automatically fall under a copyleft license. What will happen is that it will not be legal to distribute the derived work, unless the owner of the remaining work put it under a compatible license (not necessarily copyleft). If the work is distributed anyway, that is a simple copyright violation, and will not affect the license of the work."
Anthony