CAPTCHA

From Computing and Software Wiki

References

1. Luis von Ahn, Ben Maurer, Colin McMillen, David Abraham and Manuel Blum, reCAPTCHA: Human-Based Character Recognition via Web Security Measures. In Science.
2. Luis von Ahn, Manuel Blum, Nicholas Hopper, and John Langford. CAPTCHA: Using Hard AI Problems for Security. In Eurocrypt.
3. Luis von Ahn, Manuel Blum and John Langford. Telling Humans and Computers Apart Automatically. In Communications of the ACM.