Another technical “screen” without incentives design facing trouble

MathTrek: Cheating CAPTCHAs
CAPTCHAs (“completely automated public Turing test to tell computers and humans apart”!) are an increasingly common technical device to try to “keep the bad stuff out” of many services: users are asked to type in a word displayed with distortion that is easy for most humans to read, but difficult for image recognition software, before they can access various services.

Well, not too surprisingly, programmers have taken on this challenge, and software is getting better at doing the recognition and getting around the CAPTCHAs. And it turns out there’s a lot of cheap labor available for spammers and others to hire to thwart them, too.
As a general matter, technical screens are not incentive-compatible, and when the value of getting past them is reasonably high, we can expect that they will get caught up in “arms races” and rarely be highly effective against pollution.


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