IE6下PNG图片透明

<!--[if gte IE 6]>  
<script type="text/javascript">  
    function correctPNG()  
    {  
        for(var i=0; i<document.images.length; i++)  
        {  
            var img = document.images[i]  
            var imgName = img.src.toUpperCase()  
            if (imgName.substring(imgName.length-3, imgName.length) == "PNG")  
            {  
                var imgID = (img.id) ? "id='" + img.id + "' " : ""  
                var imgClass = (img.className) ? "class='" + img.className + "' " : ""  
                var imgTitle = (img.title) ? "title='" + img.title + "' " : "title='" + img.alt + "' "  
                var imgStyle = "display:inline-block;" + img.style.cssText  
                if (img.align == "left") imgStyle = "float:left;" + imgStyle  
                if (img.align == "right") imgStyle = "float:right;" + imgStyle  
                if (img.parentElement.href) imgStyle = "cursor:hand;" + imgStyle  
                var strNewHTML = "<span " + imgID + imgClass + imgTitle  
                + " style=\"" + "width:" + img.width + "px; height:" + img.height + "px;" + imgStyle + ";"  
                + "filter:progid:DXImageTransform.Microsoft.AlphaImageLoader"  
                + "(src=\'" + img.src + "\', sizingMethod='scale');\"></span>"  
                img.outerHTML = strNewHTML  
                i = i-1  
            }  
        }  
    }  
    window.attachEvent("onload", correctPNG);  
</script>  
<![endif]-->

Refer：
http://www.w3cfuns.com/forum.php?mod=viewthread&tid=297
http://www.w3cfuns.com/thread-308-1-1.html