<div id="localImag"><img id="preview" width="-1" height="-1" style="display:none" /></div>
<asp:FileUpload ID="file_head" runat="server" onchange="javascript:setImagePreview();" />

<script type="text/javascript">
function setImagePreview() {
var docObj = document.getElementById("ctl00_ContentMain_file_head");
var fileName = docObj.value;
if (!fileName.match(/.jpg|.gif|.png|.bmp/i)) {
alert('您上傳的圖片格式不正確，請重新選擇！');
return false;
}

var imgObjPreview = document.getElementById("preview");
if (docObj.files && docObj.files[0]) {
//火狐下，直接設img屬性
imgObjPreview.style.display = 'block';
imgObjPreview.style.width = '63px';
imgObjPreview.style.height = '63px';
//imgObjPreview.src = docObj.files[0].getAsDataURL();
if (window.navigator.userAgent.indexOf("Chrome") >= 1 || window.navigator.userAgent.indexOf("Safari") >= 1) {
imgObjPreview.src = window.webkitURL.createObjectURL(docObj.files[0]);
}
else {
imgObjPreview.src = window.URL.createObjectURL(docObj.files[0]);
}
} else {
//IE下，使用濾鏡
docObj.select();
docObj.blur();
var imgSrc = document.selection.createRange().text;
var localImagId = document.getElementById("localImag");
//必須設置初始大小
localImagId.style.width = "63px";
localImagId.style.height = "63px";
//圖片異常的捕捉，防止用戶修改后綴來偽造圖片
try {
localImagId.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale)";
localImagId.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = imgSrc;
} catch (e) {
alert("您上傳的圖片格式不正確，請重新選擇！");
return false;
}
imgObjPreview.style.display = 'none';
document.selection.empty();
}
return true;
}

</script>

window.URL.createObjectURL(docObj.files[0]);