rock*.jpg, road_sand*.jpg, road_sand_side.png, sky2.jpg by MiniBjorn, released under CC-BY-SA 3.0

transparence.png by samuncle released under CC-By-SA 3.0

islandtrack_signs.ac, turn_sharp_24med.png by Pixel (Wayne Dennis), released under Creative Commons Attribution - Share Alike 3.0
(This has been combined with the track model)

the track model itself is releasd under GPL.
