function ChangeCSSBgImg() {
    if (!document.getElementById) return false;

    var MyElement = "bgimg" 
    var ImgPath = "images/" 

    if (!document.getElementById(MyElement)) return false;

    var random_images = new Array ();
    random_images[0] = "main_image1.jpg"; // these are the background images
    random_images[1] = "main_image2.jpg"; 
    random_images[2] = "main_image3.jpg"; 
    random_images[3] = "main_image4.jpg"; 
    random_images[4] = "main_image5.jpg"; 
    random_images[5] = "main_image6.jpg"; 
    random_images[6] = "main_image7.jpg"; 
    random_images[7] = "main_image8.jpg"; 

    var $header = document.getElementById(MyElement);
    var $backgroundurl = $header.style.backgroundImage;
    var ImgURL = "url(" + ImgPath + random_images[rand(random_images.length)] + ")";

    if ($backgroundurl != ImgURL) {
        $header.style.backgroundImage = ImgURL; 
    }

    movement = setTimeout("ChangeCSSBgImg()",600000); 
}


/* random number generator */
function rand(n) {
    return ( Math.floor ( Math.random ( ) * n ) );
}

/* Custom onload function */
function addLoadEvent(func) {
    var oldonload = window.onload;
    if (typeof window.onload != 'function') {
        window.onload = func;
    } else {
        window.onload = function() {
            oldonload();
            func();
        }
    }
}
/* trigger onload */
addLoadEvent(ChangeCSSBgImg);