There's this paper that highlights the techniques (supposedly) including the fingerprinting: https://www.blackhat.com/docs/asia-16/materials/asia-16-Sivakorn-Im

There's this paper that highlights the techniques (supposedly) including the fingerprinting: https://www.blackhat.com/docs/asia-16/materials/asia-16-Sivakorn-Im-Not-a-Human-Breaking-the-Google-reCAPTCHA-wp.pdf https://www.blackhat.com/docs/asia-16/materials/asia-16-Siva...