title: FileUpload show waiting message while PostBack is excecuting
body: <p>For the following scenario:</p>
  
  <p>I have an ASP.NET FileUpload control and a Button that postbacks for uploading the selected file.</p>
  
  <p>I would like to know if with javascript I can:</p>
  
  <ol>
  <li>Start showing an image (loading image) when someone clicks on the button that excecutes the upload</li>
  <li>Stop showing the image when the upload of the file is complete</li>
  </ol>
  
  <p>Restrictions: I can't use ajax in this case. </p>