Development of Creative Commons licenses

["Gregory Maxwell" <gmaxwell AT gmail.com>]

I'm looking for a little clarification: Is share-alike actually the
same as copyleft?

In the recent thread on "Share-Alike with images"
(https://lists.ibiblio.org/sympa/arc/cc-licenses/2007-February/004960.html)
it was made clear that the Creative Commons is directing people that
the result of using a Share-alike licensed image in a mixed-media
whole (such as writing an article describing the image) is not
considered a derivative work, except for setting sound to video.

The historic use, and the use most people are familiar with, is the
use of copyleft in the Free Software movement, exemplified by licenses
such as the GPL. In this realm copyleft is used as a means to achieve
the goal of expanding the base of freely licensed software.

For example readline (http://en.wikipedia.org/wiki/GNU_readline) is a
software library which makes it easier to write powerful software
which interacts with users at a command line. Because readline is
GPLed, software which is written to use readline must also be GPLed
(or under a compatible free license). This has resulted in many pieces
of software being released under a free license when they might not be
otherwise, because the benefit of using readline offset the expected
returns of using a less free license.

This use of copyright to encourage the creators of other works is an
important core principle of copyleft and is a big part of how people
normally understand the purpose of copyleft. It has resulted in
criticism that copyleft licenses are 'viral', although this isn't an
accurate analogy since viruses infect more than the willing.

In the context of images, a share-alike property which never expands
past the physical pixels in the original image will mostly have the
effect of keeping crops, color-adjustments, and other trivial changes
in the free world. It will not encourage the authors of new works who
use free images out of convenience to release their new works under a
free license. While this may be a property that some (many?) desire,
it is not copyleft.

I think it would be a worthwhile discussion to discuss the merits of a
share-alike license which is not copyleft, but that's not what I'm
trying to do here.. I would like to first confirm if the cc-by-sa is
indeed not a copyleft license, or that it is not intended to be one.

Thanks for your time and consideration.