I found a bug in Supersized:
In the file 'WPSupersized.php', in the function 'clean_wpml_home_url', this statement causes me trouble:
$home_url = str_replace($search_string, '', $home_url);
$search_string = '/de' and my domain is 'desiderium.com', which makes the $home_url: http://desidrium.com/de.
$home_url after the above statement: 'http:/siderium.com'.
Obviously all the paths are wrong and images wont load.