function affiche ( pnew, prefix ) {
  if ( pnew < 1 || pnew > 99 ) { pnew = 1 ; }

  if ( pnew < 10 ) {
    image="photoscoll/" + prefix + "_G_00" + pnew + ".jpg" ; }
  else {
    image="photoscoll/" + prefix + "_G_0"  + pnew + ".jpg" ; }

   document.getElementById("photo").innerHTML="<img src='" + image + "' />";

   return true ;
}