function show_photo(URL) 
 {
  x =  (Math.round((screen.width-600)/2));
  y =  (Math.round((screen.availHeight-420)/2));
  myWindow = window.open('show_img.php?file=' + URL, 'pic', 'toolbar=no, directories=no, location=no, status=no, menubar=no, resizable=no, scrollbars=no, left='+ x + ', top= '+ y +' , width='+ 600 +', height='+ 420);
  myWindow.focus();
 }