function showPng(img){ 
   var str=String(navigator.appVersion);
	if(str.indexOf("MSIE 6")==-1) return;
//   if (navigator.appName!="Microsoft Internet Explorer") return; 
   var SC_w = img.width ;
   var SC_h = img.height;
   var imgName = img.src.toUpperCase() 
   if (imgName.substring(imgName.length-3, imgName.length) == "PNG"){  
      img.style.filter+="progid:DXImageTransform.Microsoft.AlphaImageLoader(src="+img.src+", sizingmethod=scale);"  
      img.src="js/watermark.gif"//Ϊ1px*1pxµÄ͸Ã÷gifͼƬ 
      img.width=SC_w; 
      img.height=SC_h;
	  
   }
}