[londons_explore]

> reCAPTCHA actually enters an endless selection where it's impossible to pass

I believe this is because from the same IP address there are other users who are failing the recaptcha. So in between you starting, and clicking 'submit', there are a bunch of other wrong-answer recaptchas, so, when combined with your correct answer, it looks like you got it correct just by chance, not by being a human.

[dan-robertson]

This might be true for massive sites (eg Google) but smaller sites only if the cdn aggregates traffic to many different sites.

[londons_explore]

recaptchas logic to check if someone is a bot or not is global and run on googles servers, not site specific.