What is captcha for? Separate humans from robots. What is karma needed for? Separate the "smart" and "useful" from the "stupid" and "useless." Even not so, "in order to separate the useful from the useless." But after all, captcha is also needed to separate useful people from useless robots! That is, the client, in order to prove his usefulness to the resource, it is no longer necessary just to pass the test for recognizing the text in the picture, but to perform some more complex and meaningful actions in society . Prove your ability to communicate with people. But in essence, it's just a captcha.
PS Sorry if this is obvious to someone. Personally, I just now dawned such a bright parallel.