I don't get why, when and how Google uses reCAPTCHA within their own tools. E.g. within the Webmaster Tools, I can submit up to 500 URLs for manual fetch/render and subsequent index submission. So the rate limit is already there and reasonable.
However, after 4 submitted URLs, I get a reCAPTCHA. From then on for every URL, I have to complete it with additionaly visual quizzes.
> I don't get why, when and how Google uses reCAPTCHA within their own tools.
This may or may not help with your quest.
Google triggers recaptcha when i use their search using one of my digitalocean servers as vpn and incognito mode, thus my IP address belongs to a datacentre, there isn't a cookie header and the user-agent is linux.
I had the same thing the other day. I figured maybe it was because I was in incognito mode (because logging into half of Google's properties with uBlock and Privacy Badger enabled doesn't work). sigh
However, after 4 submitted URLs, I get a reCAPTCHA. From then on for every URL, I have to complete it with additionaly visual quizzes.