4chan captcha key:
6Ldp2bsSAAAAAAJ5uyx_lx34lJeEpTLVkP5k04qc
Google supports a noscript version of the new recaptcha, described here https://developers.google.com/recaptcha/docs/faq
https://www.google.com/recaptcha/api/fallback?k=6Ldp2bsSAAAAAAJ5uyx_lx34lJeEpTLVkP5k04qc
Put this in an iframe and when the user has successfully filled in the captcha the user is told to copy paste the key into the real website field (outside the iframe, g-captcha-response)
https://www.google.com/recaptcha/api/challenge?k=6Ldp2bsSAAAAAAJ5uyx_lx34lJeEpTLVkP5k04qc
contains an image and and a field named "c" with the challenge
after the user has solved the image, do a POST to
https://www.google.com/recaptcha/api/fallback?k=6Ldp2bsSAAAAAAJ5uyx_lx34lJeEpTLVkP5k04qc
POST:
c = the challenge given
response = text response from the user
Next if the captcha was solved, get the hash inside the textarea of div.fbc-verification-token
If the textarea isn't present, the captcha wasn't solved correctly you'll reuse the received html.
next send off the reply to 4chan
POST:
g-captcha-response: HASH
Initial HTML:
reCAPTCHA-uitdaging