function bantop() {
  aux = document.URL;
  aux = aux.replace(/http:\/\/nuevo.cimav.edu.mx\//,'');
  aux = aux.replace(/\//,'-');
  document.getElementById("footer").innerHTML = '<img src="http://nuevo.cimav.edu.mx/data/files/images/imagen.jpg" alt="Imagen" />';
  alert(aux);
}