[Commons-l] Problems with derivative works

[Nilfanion]

Whilst browsing over the QI candidates page I noticed this image:
http://commons.wikimedia.org/wiki/Image:EM_Spectrum_Properties.svg.
The image itself is licensed as public domain. However it is a
derivative of two images licensed under the GFDL
(http://commons.wikimedia.org/wiki/Image:P_biology.svg and
http://commons.wikimedia.org/wiki/Image:Skyscrapercompare.svg). Unless
I am misreading something quite badly, releasing a derivative of a
GFDL-licensed work to the public domain is a violation of the GFDL.

It is easy to fix one image, but I suspect we have deeper problems
throughout the project with a lack of respect for copyleft.
Establishing just how serious this issue is will be non-trivial, never
mind resolving it.

I can think of a number of approaches to this situation, some of which
are obviously harmful to the project and/or the free content movement
as a whole.
* Ignore the terms of the GFDL (or any other copyleft licenses) in this context.
* Treat them the same as any other copyright violation.
* Contact the creator of the derivative and inform him of the
pertinent terms of the original license; and ask him to change the
licensing on the derivative.
* Changing the licensing on the derivative work to be compatible with
the original work, and inform the creator of the new work of the
change and the reason why.

Furthermore we probably have the difficulties associated with of a
CC-BY-SA work and a GFDL work being combined. I'm no lawyer, but I
suspect to truly sort these cases out will need an additional release
from some of the creators of the original works.

If we cannot enforce the copyleft terms on our own community, can we
really expect external groups to?