Have you followed the discussion on the permission for the Z-machine picture? By all means, go ahead and ask them to release it under CC-BY.
http://en.wikipedia.org/wiki/Image:Zmachine.jpg
Currently the image information page has a license which says:
"encyclopedia articles are fine. We only require a credit in the form, 'Courtesy, Sandia National Laboratories,'"
In my opinion there's nothing wrong with Wikipedia using that image even if non-encyclopec down-stream users can't. I'm sure they would allow a Wikibook too if you ask them. If you can get them to release it under CC-BY that would of course be great. And if you can get a PD image of a z-machine which is as good as this one I salute you.
Why don't you just ask them then? Since they said they only require that credit, you could ask if they mean that for ANYONE using that image. If they say anyone can use that image as long as they give that credit, then that's their "open content" license and should be allowed on Wikipedia. Since the image is of a very specific thing only existing at their labs, people would have to credit anyway.
Also, I'm a bit confused as to why it's not public domain since SNL is a government agency. Since it appears that SNL itself has control over the copyright (as opposed to the photographer who took the picture), shouldn't it be that way? I was under the impression that any works created by U.S. government employees were PD and I'd guess that if the "contractor"/photographer transfered rights over that it would be effectively the same.
---------------------------------------------- Nathan J. Yoder http://www.gummibears.nu/ http://www.gummibears.nu/files/njyoder_pgp.key ----------------------------------------------