The skydomes for the skybox were taken from:


Skybox.jpg:

http://www.gravis.com.ua/gal/content/photoprint/sky/sk_21.jpg


Skybox2.jpg:

http://www.artist-reference.com/wp-content/gallery/marlin-studios-gallery/sky-dome-panorma.jpg



I couldn't find a direct license for those photos. If there is one, please contact me.