ecco qui.

codice:
<html> 
<head>
<script type="text/javascript">
 var numphoto = 0; 

 function next() {
    numphoto = (numphoto != 20)? ++numphoto : 0;  
    document.getElementById('photo').src = numphoto + '.jpg';
 }
 
 function back() {
    numphoto = (numphoto != 0)? --numphoto : 20;  
    document.getElementById('photo').src = numphoto + '.jpg';
 }
</script> 
<head>
<body bgcolor="black"> 
[img]..\..\img\back.jpg[/img] 
[img]..\..\img\next.jpg[/img] 




[img]0.jpg[/img]  
</body> 
</html>