function swap_img(obj)
{
  var strsrc = document.getElementById(obj).src;
  var imgobj =  document.getElementById(obj);
  if (strsrc.indexOf("_off") != -1)
    {
	    var new_src = strsrc.split("_off")[0]+"_on.gif";
		imgobj.src = new_src;
    }
  else
	{
        var new_src = strsrc.split("_on")[0]+"_off.gif";
		imgobj.src = new_src;

	}

}