<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>
<script type="text/javascript">
$(document).ready(function(){
  $("#ChangeImage").click(function(){
  $('#ChangeImage').attr('src','yahoo.gif');
 
  });
});
</script>
<img src="bm_yahoo.gif" name="my_pic" id="ChangeImage">

<script type="text/javascript">
function changePic()
{
  document.getElementById("Img1").src="bm_yahoo.gif";
}
</script>
<a href="#" onclick="changePic()";><img border="0" id="Img1" src="yahoo.gif" /></a>
</script>