if (document.images) {
  
  image_on = new Image();
  image_on.src = "../images/video_on.gif";
 
  
  image_off = new Image();
  image_off.src = "../images/video.gif";
  
}

function changeImages() {
  if (document.images) {
    for (var i=0; i<changeImages.arguments.length; i+=2) {
      document[changeImages.arguments[i]].src = eval(changeImages.arguments[i+1] + ".src");
    }
  }
}