function playSlideshowAndSetCookie(page_id) {
  var slideshow_page_id = 'slideshow_page_' + page_id;
  var played_already = JSON.parse(unescape(Cookie.get(slideshow_page_id)));
  if(played_already)
    $('pic1').hide();
  else
    window.setTimeout(function(){
      new Effect.Fade("pic1",{duration:5});
      Cookie.set(slideshow_page_id, 1, 1);
    }, 5000);
}