The simplicity of it is logic defying. It used to be that you had to find crosswalks or move puzzle pieces or type blurred letters and numbers, but NOW all the sudden I can just click a box and HEY!, I'm human?
That's hardly the Turing Test I'd expected.
Cloudflare knows almost everything done from your IP address because they're used by the majority of websites. And some websites are using a cloudflare signed TLS certificate so if cloudflare wants, can see the content of the communication instead of an encrypted package
So they know if you have a human behavior (visiting many different websites at human speed and having rests during sleeping time) or if you have a bot behavior (sending millions of requests to the same endpoint at superhuman speeds)
thx, TIL