On his blog today, David Coallier has an announcement about the PEAR package he's been working on that's finally come into it's own - the Text_CAPTCHA_Numeral.
Hello all, so for the previous weeks I have put the simple pear package Text_CAPTCHA_Numeral through the rough pear proposal process and voting. Now it has been proposed, and accepted, you can see it working at this address (In it's natural form).
David also points out the live source of the demo, giving developers a great place to start with this package. There's even two FAQ questions to help get simple topics out of the way (spammers and storing the answer).