In the cost-per-click advertising model, clicks from machines are never desired and potentially fraudulent. While clicks from humans may also be fraudulent or of low quality, we believe distinguishing humans from machines would be a large step forward in the fight against ad fraud. Traditional CAPTCHAs, however, can be annoying and awkward to use, especially on UI-limited devices such as cell phones. In this talk, we introduce Clickable CAPTCHAs, which increase the usability of CAPTCHAs while offering comparable levels of security. We discuss some applications to ad fraud.
Chow, R. ; Golle, P. ; Jakobsson, M. ; Wang, X. Clickable CAPTCHAs. AdFraud '07 Workshop; 2007 September 14; Stanford, CA, USA