How to Use Loader image in ajax

<asp:UpdatePanel ID="uppnl_Select_File_Format" runat="server" UpdateMode="Conditional">
<ContentTemplate&g开发者_如何转开发t;
          <div class="button-bg-2">
                            <div class="button-text-2">
                                <asp:LinkButton ID="btnCreate" ValidationGroup="CreateVersion" runat="server" OnClick="btn_Create_OnClick"
                                    CausesValidation="true">Add Title</asp:LinkButton>
                            </div>
                        </div>
</ContentTemplate>
        <Triggers>
            <asp:PostBackTrigger ControlID="btnCreate" />
            <asp:AsyncPostBackTrigger ControlID="ddlstMedia" />
        </Triggers>
    </asp:UpdatePanel>
    <asp:UpdateProgress  ID="upprogpnl" runat="server" AssociatedUpdatePanelID="uppnl_Select_File_Format">
        <ProgressTemplate>
            <asp:Image ID="img_Loading" runat="server" ImageUrl="~/App_Themes/Admin/LoadingImages/loading1.gif" />
        </ProgressTemplate>
    </asp:UpdateProgress>

Loader image is not shown when button click event ...

Please reply me clearly, i'm a beginner......

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thisi is the code for showing loader gif in time of processing

   <ProgressTemplate>

       <div   Style="z-index: 105; left: 450px;position: absolute; top: 230px" > 
       <center>
           <img  id="imgloader" runat="server" src="images/loading.gif" />
         </center>
       </div>

   </ProgressTemplate>

.