This is a bit off-topic, but I'm surprised that the NASA image is listed as CC-BY. I was under the impression that NASA imagery was public domain by default.
Their website [1] says "NASA content [...] generally are not copyrighted." It then goes on to say that "NASA should be acknowledged as the source of the material." IANAL, but I would assume that if the data is not copyrighted, then there's no need to attribute the source, making that "should" pretty toothless.
Note the "generally" there. Further down it says explicitly "NASA material is not protected by copyright unless noted". In their Flickr page they have selected the CC BY-NC 2.0 license so this works, I think, as a notice of copyright that at the same time grants you a license to use the image (provided you follow the terms of said license).
It's easy to imagine that NASA has more limited rights to reproduce and redistribute images produced by their partners though, and they have lots of partners.
Their website [1] says "NASA content [...] generally are not copyrighted." It then goes on to say that "NASA should be acknowledged as the source of the material." IANAL, but I would assume that if the data is not copyrighted, then there's no need to attribute the source, making that "should" pretty toothless.
[1] http://www.nasa.gov/multimedia/guidelines/index.html