Since various Google products and domains are blocked in China and probably other countries, reCAPTCHA does not work in phpBB at this time. Unfortunately, users in some countries are unable to register and do other things using reCAPTCHA on boards that use it.
Could you please update the software to use `www.recaptcha.net` instead of `www.google.com` in the reCAPTCHA insertion code to circumvent blocking in some countries?
Alternatively, could you add a checkbox option to use this alternate domain?
This approach is described in the reCAPTCHA FAQ:
See the heading "Can I use reCAPTCHA globally?"