Analyzing CAPTCHAs 105
Bruce Schneier's blog pointed me to a research paper on
"Attacks and Design of Image Recognition CAPTCHAs" (PDF). The abstract says, "We systematically study the design of image recognition CAPTCHAs (IRCs) in this paper. We first review and examine all IRCs schemes known to us and evaluate each scheme against the practical requirements in CAPTCHA applications, particularly in large-scale real-life applications such as Gmail and Hotmail."
Re:hmm... (Score:5, Interesting)
Well, CAPTCHAs worked because they relied on vision tests - a skill that humans still do better than computers, but computer vision is already quite advanced. Then the countermeasures came where CAPTCHAs started getting so distorted that it was impossible to determine the code (I remember a forum I signed up for - too more than 15 tries and a cookie reset).
However, there are still difficult-for-computer-but-easy-on-humans tasks that can be done. I'm surprised no one's yet hooked a way into the Amazon Mechanical Turk or the like. Perhaps a simple one can be where you show a panoramic view along a busy street. Then you ask the question "What is the name of the store at number 763?" Or "What is the street number of ZZZ Supermarkets along this street?". "There is a large group of friends gathered near XXX store. How many people are in the group?"
Or simpler ones - if your forum or other thing is about a specific topic, ask a question about that topic. Or even self-referential ones. "What of the following will an art thief steal? A) Mona Lisa, B) Big screen HDTV, C) Cellphone, D) Money".
Might as well advance the state of things like image recognition and natural language queries while we're at it.