A loading image is shown as a progress indication when an AJAX request is performed, i.e. when the page is loading silently. This improves the look and feel of the page as there are no sudden changes and unnecessary flickering.

The example demonstrates all present loading images coming with the ajax controls.

You can set your own picture as a loading image, just show the path to it in the loading panel definition:

<rad:AjaxLoadingPanel id="LoadingPanel1" Runat="server">
  <asp:Image id="Image1" runat="server" ImageUrl="~/RadControls/AJAX/Skins/Default/loading1.gif" >
  </asp:Image>
</rad:AjaxLoadingPanel>