[trickui]

Ne trovi centinaia di tutorial che uasano GD, come questi
http://www.codewalkers.com/c/a/Misce...TCHA-with-PHP/

http://fossaweb.net/103/php/come-cre...ptcha-con-php/

http://www.w3facile.com/php/verifica...-tutorial.html

Ciao