Google reCAPTCHA in China
As google says in his assistance page, you should use this domain "www.recaptcha.net" instead "www.google.com" on the api call.
- First, replace src="https://www.google.com/recaptcha/api.js" with src="https://www.recaptcha.net/recaptcha/api.js"
- After that, apply the same to everywhere else that uses "www.google.com/recaptcha/" on your site.
Obtained from: https://developers.google.com/recaptcha/docs/faq#can-i-use-recaptcha-globally
Edit: to clarify on some of the comments, while if you try it outside of china yes you do get references to gstatic.com but if you try this in china, any references to gstatic.com are replaced with gstatic.cn (don't forget to add it to your SCP). So this solution is still valid.
IMHO, google things are not stable in China as it can be blocked anytime. From Baidu threads, it also mentioned that sometime google recaptcha works, sometime it doesn't. https://www.v2ex.com/t/492752 (Chinese)
In programming world ,unstable function means useless or more code for dealing with exception.
If you really need to use google recaptcha, you would better test properly using VPN (IP in China) first.
Here are some options you can consider,
You can use alternative captcha
Google will tell you various captcha.
Build your own captcha
Open Source Invisible reCAPTCHA alternatives
- Use proxy web server(nginx) to send and receive data to or from google recaptcha