On request, I am posting a patch for Wakaba which enables the use of reCAPTCHA. It depends on the CPAN module Captcha::reCAPTCHA which means you'll probably have difficulty using this patch on shared hosting. I apologise for that, but I'm a novice programmer and don't know any other way of doing it. Debian/Ubuntu users with root access can install the module using sudo apt-get install libcaptcha-recaptcha-perl. Dreamhost has instructions for setting up CPAN without root access on their wiki.

To apply the patch, use patch -p1 -i waka_recaptcha.patch. To enable it, set ENABLE_CAPTCHA in config.pl to ENABLE_CAPTCHA => 'recaptcha'. You also need to set your private and public key from the reCAPTCHA website.

In the case that the required CPAN module is unavailable, it will bypass the CAPTCHA check altogether. I'm not sure whether this is a good decision or not. If you can, please improve this patch so it doesn't depend on the above-mentioned module.