Re: Where can I get this picture for free?
You're right, all NASA images are in the public domain. That doesn't mean that people can't package them and sell them. They're making money from a "value-added service".
Your biggest problem finding it in the NASA archives is identifying it. There are millions of NASA images. If you could at least figure out the mission, you could try spaceflight.nasa.gov. Also, the Kennedy PAO has a huge collection, at ksc.nasa.gov.
Good luck, man. You'll need it!
--Robert