txrecaptcha is a Twisted-based reCAPTCHA client.
Unlike the official Google Python recaptcha-client, which is hardcoded to use plaintext HTTP, txrecaptcha always uses TLS with strict hostname checking (for Twisted<=13.2.0) or certificate pinning (for Twisted>=14.0.0).
Small portions of this code were taken from the official Google Python recaptcha-client module, version 1.0.6. Those portions are RecaptchaResponse, API_SERVER, They total 5 lines of code, which are copyright the authors of the recaptcha-client package.