here is simple example
<asp:Panel ID="Panel6" runat="server" Height="50px" Style="z-index: 100; left: 10px;
position: absolute; top: 10px" Width="125px">
<asp:UpdateProgress ID="UpdateProgress1" runat="server" DisplayAfter="1">
<ProgressTemplate>
<span style="color: #ff00ff">
<asp:Image ID="Image1" runat="server" ImageUrl="~/images/spinner.gif" Width="32px" /></span>
</ProgressTemplate>
</asp:UpdateProgress>
</asp:Panel>
now add script manager and update panel
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:UpdatePanel ID="UpPanel1" runat="server">
<ContentTemplate>
now when page is post back update progress bar show the image.