Replace Garnett image with Columbia image

Replace Garnett image with Columbia image

To clear up licensing issues, change to an image used on the Wikimedia
Commons [1].  I actually grabbed a slightly different, higher
resolution image directly from NASA [2], which is linked from their
Columbia page [3].  Using this image as an example of cutting edge
technology is ammusing, because NASA deprecated the system in 2013.  A
few details [3]:

  Location: NASA Advanced Supercomputing facility at Ames Research
            Center
  Peak (2008) specs:
    Nodes:                   SGI Altix 3700 and 4700
    Processors:              Intel Itanium 2
    Cores:                   18,824
    Memory:                  27 terabytes
    Theoretical performance: 82.9 teraflops
    Operating system:        SUSE Linux Enterprise

NASA's media usage guidelines [4], reproduced in full:

  NASA still images; audio files; video; and computer files used in
  the rendition of 3-dimensional models, such as texture maps and
  polygon data in any format, generally are not copyrighted. You may
  use NASA imagery, video, audio, and data files used for the
  rendition of 3-dimensional models for educational or informational
  purposes, including photo collections, textbooks, public exhibits,
  computer graphical simulations and Internet Web pages. This general
  permission extends to personal Web pages.

  This general permission does not extend to use of the NASA insignia
  logo (the blue "meatball" insignia), the retired NASA logotype (the
  red "worm" logo) and the NASA seal. These images may not be used by
  persons who are not NASA employees or on products (including Web
  pages) that are not NASA-sponsored.

  NASA should be acknowledged as the source of the material except in
  cases of advertising. See NASA Advertising Guidelines.

  If the NASA material is to be used for commercial purposes,
  especially including advertisements, it must not explicitly or
  implicitly convey NASA's endorsement of commercial goods or
  services. If a NASA image includes an identifiable person, using the
  image for commercial purposes may infringe that person's right of
  privacy or publicity, and permission should be obtained from the
  person. Any questions regarding application of any NASA image or
  emblem should be directed to:

    Photo Department
    NASA Headquarters
    300 E St. SW
    Washington, DC 20546
    Tel: 202-358-1900
    Fax: 202-358-4333

  Linking to NASA Web Sites

  NASA Web sites are not copyrighted, and may be linked to from other
  Web sites, including individuals' personal Web sites, without
  explicit permission from NASA. However, such links may not
  explicitly or implicitly convey NASA's endorsement of commercial
  goods or services.

  NASA images may be used as graphic "hot links" to NASA Web sites,
  provided they are used within the guidelines above. This permission
  does not extend to use of the NASA insignia, the retired NASA
  logotype or the NASA seal.

  NASA should be acknowledged as the source of the material except in
  cases of advertising. See NASA Advertising Guidelines.

  Restrictions

  As a government entity, NASA does not license the use of NASA
  materials or sign licensing agreements. The agency generally has no
  objection to the reproduction and use of these materials (audio
  transmissions and recordings; video transmissions and recording; or
  still and motion picture photography), subject to the following
  conditions:

  * NASA material may not be used to state or imply the endorsement by
    NASA or by any NASA employee of a commercial product, service, or
    activity, or used in any manner that might mislead. Please see
    NASA Advertising Guidelines and Merchandising Guidelines for more
    information.

  * It is unlawful to falsely claim copyright or other rights in NASA
    material.

  * NASA shall in no way be liable for any costs, expenses, claims, or
    demands arising out of the use of NASA material by a recipient or
    a recipient's distributees.

  * NASA does not indemnify nor hold harmless users of NASA material,
    nor release such users from copyright infringement, nor grant
    exclusive use rights with respect to NASA material.

  * NASA material is not protected by copyright unless noted. If
    copyrighted, permission should be obtained from the copyright
    owner prior to use. If not copyrighted, NASA material may be
    reproduced and distributed without further permission from NASA.

  * If a recognizable person, or talent (e.g., an astronaut or a noted
    personality engaged to narrate a film) appears in NASA material,
    use for commercial purposes may infringe a right of privacy or
    publicity. Therefore, permission should be obtained from the
    recognizable person or talent. If the proposed use of the NASA
    material could be viewed as a commercial exploitation of that
    person. However, if the intended use of NASA material is primarily
    for communicative purposes, i.e., books, newspapers, and magazines
    reporting facts of historical significance (constitutionally
    protected media uses), then such uses will generally be considered
    not to infringe such personal rights.

  * Some NASA audiovisual material may incorporate music or footage,
    which is copyrighted and licensed for the particular NASA
    work. Any editing or otherwise altering of the work may not be
    covered under the original license, and therefore would require
    permission of the copyright owner.

  * NASA audiovisual material may include visible NASA identifiers
    (e.g., the name of the vehicle and the NASA Insignia or Logotype
    in photographs or film footage of Space Shuttle vehicles). Use of
    such materials is generally non-objectionable, provided the NASA
    identifiers appear in their factual context.

I think that the recognizable NASA logo on the picture itself, the
fact that I'm showing the picture inside a link to NASA's Columbia
page, and this commit message should satisfy "NASA should be
acknowledged as the source of the material".

[1]: http://commons.wikimedia.org/wiki/File:Us-nasa-columbia.jpg
[2]: http://www.nas.nasa.gov/hecc/assets/images/content/Columbia_fisheye_large.jpg
[3]: http://www.nas.nasa.gov/hecc/resources/columbia.html
[4]: http://www.nasa.gov/audience/formedia/features/MP_Photo_Guidelines.html#.Utm2dvGIa00