I am fairly certain that ReCAPTCHA does many things behind the scenes. It probably is using webGL and many other browser features to "fingerprint" your browser, OS, graphics card, sound card, etc. This is simple by just for example drawing some polygons in the background then reading the frame buffer, because different graphics cards / drivers may output different buffers slightly. Then it can store that fingerprint to show you less ReCAPTCHA in the future if you successfully pass the first one. This will also link that fingerprint with all other websites which use google analytics and now they have your full browsing history. The TOS may specify they are not _sharing_ that information, but they can do whatever they want internally to fully mine that data.

Well on top of that you train the image recognition algorithms of a tech giant. So for them it is a win-win strategy: user data and free labour

ReCAPTCHA basically looks up your google account and checks your browsing history and if your IP looks "spammy" to determine if you are a bot. The actual challenge is just a data mining operation and isn't meant to actually prove if you are a human because if it has determined you are not a human it won't let you through even if you do 10 challenges correctly.

Theoretocally it might use signals when you are logged in, but Recaptcha also works when you are not logged into google. So, not really.

Just because login isn't required, dosen't mean its not recorded.

No, that's how it used to be. Now with ReCaptcha v3 the recommend you load it on all your pages, not just the forms you are trying to protect, so they can predict friend vs foe more accurately.

Or rather keep Google tracking cookies alive forever and updated.

So how does one block this?

Firefox and uMatrix[0], and then never go to those sites again, because you won't be able to use them anyway. Whether or not you want to contact the owner of the site and tell them what's up is up to you.

[0]: https://addons.mozilla.org/en-US/firefox/addon/umatrix/