function ch(i)
{
            var backImage = new Array();
            backImage[0] = "11.jpg";
            backImage[1] = "22.jpg";
            backImage[2] = "33.jpg";
            backImage[3] = "tv.png";
document.body.background = backImage[i];

}

            function ch_image()
            {
                for(i=0;i<4;i++)
                {
            setTimeout("ch(i)",10000);
                }
            }