function toggle_visibility(id) {
       var e = document.getElementById(id);
       if(e.style.display == 'block') {
          e.style.display = 'none';
		  document.getElementById('hidebtn').style.backgroundImage="url('img/tit_credits_plus.gif')";
	   } else {
          e.style.display = 'block';
		  document.getElementById('hidebtn').style.backgroundImage="url('img/tit_credits_min.gif')";
       }
	}