images = new Array(7);

images[0] = "<style type='text/css'>body{ background: transparent url(http://tauchclub-ostrhauderfehn.de/neueseite/hintergrund/back1.jpg) fixed 50% 0;}</style>";

images[1] = "<style type='text/css'>body{ background: transparent url(http://tauchclub-ostrhauderfehn.de/neueseite/hintergrund/back2.jpg) fixed 50% 0;}</style>";

images[2] = "<style type='text/css'>body{ background: transparent url(http://tauchclub-ostrhauderfehn.de/neueseite/hintergrund/back3.jpg) fixed 50% 0;}</style>";

images[3] = "<style type='text/css'>body{ background: transparent url(http://tauchclub-ostrhauderfehn.de/neueseite/hintergrund/back4.jpg) fixed 50% 0;}</style>";

images[4] = "<style type='text/css'>body{ background: transparent url(http://tauchclub-ostrhauderfehn.de/neueseite/hintergrund/back5.jpg) fixed 50% 0;}</style>";

images[5] = "<style type='text/css'>body{ background: transparent url(http://tauchclub-ostrhauderfehn.de/neueseite/hintergrund/back6.jpg) fixed 50% 0;}</style>";

images[6] = "<style type='text/css'>body{ background: transparent url(http://tauchclub-ostrhauderfehn.de/neueseite/hintergrund/back7.jpg) fixed 50% 0;}</style>";

index = Math.floor(Math.random() * images.length);

document.write(images[index]);