function ChangeImage(s)                                                                                                             
{                                                                                                                                   
  var nom_image = "img_"+s+"_ws.gif";                                                                                               
  imgws = new Image();                                                                                                              
  var jourdhui = new Date();                                                                                                        
  var heure = jourdhui.getTime();                                                                                                   
  imgws.src = "images/"+heure+nom_image;                                                                                               
}