var images = [
        'images/qas_1.png',
        'images/qas_2.png',
        'images/qas_3.png',
        'images/qas_4.png'
    ];
    var cnt = images.length;

    $(function() {
        setInterval(Slideshow, 300);
    });

    function Slideshow() {
        $('#slideshow').fadeout("slow", function() {
            $(this).attr('src', images[(images.length++) % cnt]).fadeIn("slow");
        });
    }