Monday, August 16, 2010

Economics of CAPTCHA

If you use the web, you have undoubtedly encountered a CAPTCHA, which is text that is designed to be difficult for computers to read but easy for humans. In this paper, the authors examine the economics of CAPTCHA; that is, they examine the utility of this approach in light of the emergence of "deCAPTCHA" services, which rely on either computer software or human readers (or both) in an attempt to defeat the CAPTCHA images. Doing this allows the authors to view the underlying phenomenon in a different light and argue that CAPTCHAs
... should more properly be regarded as an economic [impediment], as witnessed by a robust and mature CAPTCHA-solving industry which bypasses the underlying technological issue completely. Viewed in this light, CAPTCHAs are a low-impact mechanism that adds friction to the attacker’s business model and thus minimizes the cost and legitimate user impact of heavier-weight secondary defenses. CAPTCHAs continue to serve this function, but as with most such defensive mechanisms, they simply work less efficiently over time.

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