var xPos = 300;
var yPos = 200; 
var step = 1;
var delay = 30; 
var height = 0;
var Hoffset = 0;
var Woffset = 0;
var yon = 0;
var xon = 0;
var pause = true;
var interval;
img1.style.top = yPos;
function changePos() 
{
width = document.body.clientWidth;
height = document.body.clientHeight;
Hoffset = img1.offsetHeight;
Woffset = img1.offsetWidth;
img1.style.left = xPos + document.body.scrollLeft;
img1.style.top = yPos + document.body.scrollTop;
if (yon) 
   {yPos = yPos + step;}
else 
   {yPos = yPos - step;}
if (yPos < 0) 
   {yon = 1;yPos = 0;}
if (yPos >= (height - Hoffset)) 
   {yon = 0;yPos = (height - Hoffset);}
if (xon) 
   {xPos = xPos + step;}
else 
   {xPos = xPos - step;}
if (xPos < 0) 
   {xon = 1;xPos = 0;}
if (xPos >= (width - Woffset)) 
   {xon = 0;xPos = (width - Woffset);   }
}

function start()
{
img1.visibility = "visible";
   interval = setInterval('changePos()', delay);
}
function pause_resume() 
{
   if(pause) 
   {
    clearInterval(interval);
    pause = false;}
   else 
   {
    interval = setInterval('changePos()',delay);
    pause = true; 
    }
   }
start();