var out="";
var limg="";

function off() {

  if (out=="") { return; }

  if (document.images) {
    document.images[limg].src=out;
    out="";
  }
}

function on(img,o1,o2) {
  if (document.images) {

  if (out != "") { off(); }

    document.images[img].src=o1;
    out=o2;
    limg=img;
  }
}