function changeImage() {
    var $alt = $('#home_pictures IMG.obersteebene');

    if($alt.next().length)
        var $neu = $alt.next();
    else
        var $neu = $('#home_pictures IMG:first');

    $alt.addClass('mittlereebene');
    $alt.removeClass('obersteebene');
    $neu.css({
        opacity: 0.0
    });
    $neu.addClass('obersteebene');

    $neu.animate({
        opacity: 1.0
    }, 2000, function() {
        $alt.removeClass('mittlereebene');
    });
}