[Javascript] Img posiition?

[FRANCESC ESCOFET]

  Sorry folks 
  anybody knows how I can get the position (top and left) of a img?

  this dont work---

  <script>
   alert (document.all['my_img'],style.pixelTop);  // this alert return 0
   alert (document.all['my_img'],style.pixelLeft); // this alert return 0
  </script>

  <img id="my_img" src="my_img.gif">