js :实现图片上传前,预览客户端图片（兼容IE6和IE7）

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
    <title>无标题页</title>
       <script type="text/javascript" src="../js/jquery.js" charset="gb2312"></script>
<script type="text/javascript">
function preview()
{
    var picId = $("#picId").val();
    alert(picId);
    var fileext=picId.substring(picId.lastIndexOf("."),picId.length);
    fileext=fileext.toLowerCase();
    $("#fileext").val(fileext);
    if ((fileext!='.jpg')&&(fileext!='.gif')&&(fileext!='.jpeg')&&(fileext!='.bmp'))
    {
        alert("对不起，系统仅支持标准格式的照片，请您调整格式后重新上传，谢谢 !");
        $("#picId").focus();
    }
    else
    {
        $("#newPreview").html('');
        var newPreview =$("#newPreview")[0];
        var imgDiv = document.createElement("div");
        document.body.appendChild(imgDiv);
        imgDiv.style.width = "180px";    imgDiv.style.height = "140px";
        imgDiv.style.filter="progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod = scale)";
        imgDiv.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = picId;
        newPreview.appendChild(imgDiv);
    }
}
</script>
</head>
<body>
<input name="uploadFile" type="file" class="input_width" id="picId" maxlength="50" onchange="preview()"/>
（推荐上传图片像素大小为180*140)
<div id="newPreview"></div>
</body>
</html>