CAPTCHAs: The Good, the Bad, and the Ugly

A CAPTCHA is a program that generates challenges that are easy to solve for humans but difficult to solve for computers. The most common CAPTCHAs today are text-based ones where a short word is embedded in a cluttered image. In this paper, we survey the state-of-the-art of currently deployed CAPTCHAs, especially of some popular German sites. Surprisingly, despite their importance and the largescale deployment, most of the CAPTCHAs like the ones of the "Umweltpr

• Type: Journal
• Year: 2010
• Where: SICHERHEIT
• Authors: Paul Baecher, Marc Fischlin, Lior Gordon, Robert Langenberg, Michael Lützow, Dominique Schröder
• Keywords: Captchas, Common Captchas, Popular German Sites, Security Privacy, SICHERHEIT 2010