ASP.NET Webforms image does not display on post back pin

<div style="float: left; width: 122px; vertical-align: baseline;">
<dx:ASPxUploadControl ID="uplImage" runat="server" ClientInstanceName="uploader"
>
<clientsideevents fileuploadcomplete="function(s, e) { Uploader_OnUploadComplete(e); }"
="" fileuploadstart="function(s, e) { Uploader_OnUploadStart(); }">
<validationsettings allowedcontenttypes="image/jpeg,image/gif,image/pjpeg,image/bmp"
="" allowedfileextensions=".jpg,.jpeg,.jpe,.gif,.bmp" maxfilesize="4000000">


</div>
<div style="float: left; width: 45px; vertical-align: baseline;">
<dx:ASPxButton ID="btnUpload" runat="server" AutoPostBack="False" CausesValidation="false"
ClientInstanceName="btnUpload" Text="Upload" ToolTip="Allowed image types: jpeg, gif,bmp and Maximum file size: 4Mb"
TabIndex="9" Width="45px">
<clientsideevents click="function(s, e) { uploader.UploadFile(); }">

</div>

<td rowspan="6">
<img id="previewImage" runat="server" alt="" src="~/Images/user.JPG" style="width: 150px;
height: 150px" />
</td>




<script language="javascript" type="text/javascript">
function Uploader_OnUploadStart() {
//alert("Hi");
btnUpload.SetText("Uploading...");
btnUpload.SetEnabled(false);
}
function Uploader_OnUploadComplete(args) {
var imgSrc = aspxPreviewImgSrc;
if (args.isValid) {
var date = new Date();
imgSrc = '<%=ResolveUrl("~/UploadedImages/") %>' + args.callbackData; //"UploadedImages/" + args.callbackData; //+ "?dx=" + date.getTime();
}
getPreviewImageElement().src = imgSrc;
btnUpload.SetEnabled(true);
btnUpload.SetText("Upload");
}
function getPreviewImageElement() {
return _aspxGetElementById('<%=previewImage.ClientID%>'); //("previewImage");
}
var aspxPreviewImgSrc = (getPreviewImageElement() != null) ? getPreviewImageElement().src : null;
</script>

server side code

protected string SavePostedFile(UploadedFile uploadedFile)
{
string ret = "";
if (uploadedFile.IsValid)
{
//String NewFileName = Guid.NewGuid().ToString() + Path.GetExtension(uploadedFile.FileName);
String NewFileName = Session.SessionID + Path.GetExtension(uploadedFile.FileName);
String tempFileName = MapPath(UploadDirectory) + NewFileName;
StoreSessionState(UPLOADEDIMGNAME, tempFileName);
uploadedFile.SaveAs(tempFileName);
ret = NewFileName;
}
return ret;
}