I actually have some bots which scrape Google sites (for the purpose of integrating stuff like Google Keep into KRunner), and they just use the Useragent of a regular phone, send normal POST data, etc. Works perfectly fine, and — I just checked — this bot is recognized as normal user by this captcha system. No Captcha input.

I tried it even with a new Google profile and just using cURL to log into Google, then started a new browser session and imported the cookies from cURL. Worked just as well.

I guess this makes it easier for malicious bot-authors...