Tomasz-
if you're putting such image on GFDL-ed article
you're breaking copyright
of authors of the article - they didn't give you permisions to distribute
non-GFDL derivates of their work.
See my response to Marco.
We also have to make it legal to distribute Wikipedia
in Europe, which have
different copyright laws, especially when it comes to what in USA is
called "fair use", and what is usually described explicitely by copyright
laws.
We should make reasonable efforts to do so, but fortunately, most
countries have fair use equivalents. For example, in Germany the use of an
image is called a "Großzitat", and currently allowed in scientific works
(including popular scientific ones).
Our primary concern, however, especially regarding the English Wikipedia,
is for US law.
Regards,
Erik