picture lisensed at :
     http://creativecommons.org/licenses/by-sa/2.0/deed.en
     http://creativecommons.org/licenses/by/2.0/deed.en
    
    URL:
a.png		http://www.flickr.com/photos/libertinus/891434640/sizes/z/in/photostream/
b.png		http://www.flickr.com/photos/hamed/281311122/sizes/z/in/photostream/
c.png		http://www.flickr.com/photos/55948751@N00/3831916479/sizes/m/in/photostream/
d.png		http://www.flickr.com/photos/theklan/1276710183/sizes/z/in/photostream/
socratesg.png	http://en.qi-hardware.com/wiki/File:Socratesg.png