for(var i = 1; i < 19; i++) 


document.write('<div class="thumb"><a href="javascript: void window.open(\'picture.php?x='+i+'\',\'gallery\',\'toolbar=0,directories=0,status=0,menubar=0,scrollbars=0,resizable=0,width=620,height=630\')";><img src="images/tumb'+i+'.jpg"></a></div>');