function getBackground(){

    var bgimg = new Array();
    bgimg[0] = "images/background1.png";
    bgimg[1] = "images/background2.png";
    bgimg[2] = "images/background3.png";
    
    var random = Math.floor(Math.random() * bgimg.length);
    var imgurl = bgimg[random];
    document.body.style.backgroundImage = 'url(' + imgurl + ')';
}