reCAPTCHA[NoCAPTCHA]验证码申请地址

reCAPTCHA是Google旗下的验证码系统.
reCAPTCHA同时免费提供给第三方网站使用

具体介绍看维基百科

https://zh.wikipedia.org/wiki/ReCAPTCHA

这里给出申请地址,请自行查看

https://www.google.com/recaptcha/admin

https://recaptcha.net/
<script src='https://www.recaptcha.net/recaptcha/api.js'  defer></script>

<script src="https://www.recaptcha.net/recaptcha/api.js?onload=renderGoogleInvisibleRecaptcha&render=explicit" async defer></script>

补充网上整合资源

https://www.codexworld.com/new-google-recaptcha-with-php/
http://blog.sina.com.cn/s/blog_8cf4ddf40100xyre.html
https://github.com/google/recaptcha
https://stackoverflow.com/questions/41079335/implement-the-new-invisible-recaptcha-from-google