entete setRequestHeader envoi de fichier

function AjoutePhoto()   
{   
  var sel = document.getElementById('inser_photo');
  if( sel != null )
  {
    document.getElementById('DIVattente').innerHTML= "<center><img src='/images/animes/attente.gif' title='En chargement...' /></center>";
    if( sel.files.length == 1 )
    {
      var variable = encodeURIComponent(sel.files[ 0 ].getAsBinary());
 
      var xhr = GetXHR();
      var url = "http://www.payebook.com/html/requete-ajax.php" ;
      xhr.open("POST",url,false);
      xhr.setRequestHeader("Content-Type", "multipart/form-data; boundary=111222111");
      var Photo = 'photo=push&filename=' + sel.files[ 0 ].fileName + '&filesize=' + sel.files[ 0 ].fileSize + 
              '&binary=' + variable;
      xhr.send( Photo );
      if(xhr.readyState == 4 && xhr.status == 200)
      {
        leselect = xhr.responseText;
      }
    }
  }
  document.getElementById('DIVattente').innerHTML= "Fichier copie";
}

if( sel.files.length == 1 )

 xhr.setRequestHeader("Content-Type", "multipart/form-data; boundary=111222111");

<form action = "action.php" enctype = "multipart/form-data" method = "POST" target = "frame_cachee">
  <input type = "file"   id = "fichier" name = "fichier">
  <input type = "submit" id = "btn" value = "Envoyer">
</form>
<iframe name = "frame_cachee" style = "display:none;" src = ""></iframe>