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

var MyElement = "maindiv" //The ID of the element you want to change
var ImgPath = "img_index/full_image/" //The file path to your images

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

var random_images = new Array ();
random_images[0] ="launch.jpg";
random_images[1] ="broder_1.jpg";
random_images[2] ="alrg_missle_dest.jpg";
random_images[3] ="STEALTH_karl_drage.jpg";
random_images[4] ="phantom_1.jpg";
random_images[5] ="phantom_2.jpg";
random_images[6] ="stealth_ks.jpg";
random_images[7] ="tom_cat.jpg";
random_images[8] ="missile_crusier.jpg";
random_images[9] ="hell_cat.jpg";
random_images[10] ="take-off.jpg";
random_images[11] ="hedgehog.jpg";
random_images[12] ="tom_kat.jpg";
random_images[13] ="jet_banking.jpg";
random_images[14] ="zmaster_surfing_2.jpg";
random_images[15] ="abel_1.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()",5000);     /* 8000 */
}

/* 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);