验证码解决方案

https://github.com/inorganik/ImagelessCaptcha 
How is three-hundred and seven written as a number?

https://www.phpcaptcha.org/try-securimage/ 
可以听语音的验证码

https://visualcaptcha.net/ 
图像选择和语音验证码

https://github.com/vincenting/campto 
汉字和数字结合计算的验证码

http://www.josscrowcroft.com/demos/motioncaptcha/ 
画图验证

https://jessekorzan.github.io/rUhuman/ 
滚动条计算验证码

https://github.com/ARCANEDEV/noCAPTCHA 
简单粗暴，基于谷歌，国内无法使用