This is a demo for attributes "width" and "height" of the type="image" input field in the Forms.

　HTML:

  <input type="image" id="im" width="100" height="100" src="flower.png"/>
  <script>
    function changesize(){
      var e = document.getElementById("im");
      e.width="200";
      e.height="200";
    }
    setTimeout(changesize,2000);
  </script>