var timer_expired = true;
var image_loaded = false;

var i = 0;

function loaded() {
 if (i != 2)
  
  {
    if (timer_expired) {
      document.visible.src = document.hidden.src;
      image_loaded = true;
      timer_expired = false;
      setTimeout('timeout()',4000);
      document.visible.src = 'image' + (i++) + '.jpg';
    }
  
  
    else {
      image_loaded = true;
    }
  }
}

function timeout() {
  timer_expired = true;
  if (image_loaded) 
  {
    loaded();
  }
}