Why must I prove to a machine that I am a human?

Question

From time to time I am urged to click through so-called captchas in order to prove to the machine that I am a human when posting answers.

The captchas often are not precise:

E.g., some minutes ago I was asked/urged to click on all images that show vehicles although no image showed a vehicle at all while many images - like puzzle pieces - showed parts of a vehicle.

What is going on here?

Why the heck do I have to prove to such an imprecise virtual instance that I am a real human??? ;-) ;-(

Am I to feel comfortable about having to prove my existence as a real human being to a virtual instance?

There is this movie "A beautiful mind". There is a scene where John Nash is addressed by a student and asks another student whether that other student too can see the student addressing him. If a human being for some reasons wishes to make sure that I am real, that's okay to me.

But with these captchas I am not faced to a human. Here I am faced to a machine-driven program whose conversation is -eh- virtual and not even precise.
This means: I have to prove my real existence to a virtual instance.

I really take umbrage when virtual instances behave like this towards me. ;-)

Answer 1

From The Complete Rate-Limiting Guide

Users with ≥ 10k rep trip CAPTCHA* if more than once per 30 seconds, or within 5 seconds of starting new post

The idea behind this is that even high reputation users should spend some time writing their answers. Note that those 5 seconds include situations where the answer is saved as a draft, you reload the page and hit the submit button within 5 seconds. Or if you write the post in a text editor, copy/paste it into the answer box and hit the submit button within 5 seconds. So I agree it's not an ideal system.

Additionally, you could run into captchas when there is some spam being posted from the same IP address as you. You could try using a VPN or hotspot to avoid this.