Understanding CAPTCHA-Solving Services in an Economic Context 6: Q&A Part at USENIX

Drawing a line under the presentation, Marti Motoyama takes questions from the USENIX audience about CAPTCHAs proper and the related solving services.

Question: You said that one of your goals when you were doing this research was maybe to figure out something about the workforce that you can take advantage of, to maybe make CAPTCHAs more effective. So, is there anything that you can say about what you’ve learned towards that goal?

Marti Motoyama at USENIX Security '10 Answer: Well, you might want to think about making a culturally sensitive CAPTCHA, one that perhaps people from the United States might know an answer to. And we’ve actually seen that deployed in practice. And actually, to sign up for some of these services, for example, you need to be able to read Russian and answer a specific question about who the Prime Minister of Russia is. So you might envision a solution that takes that into account, because if you make it so that the workers really have to understand something unique to a particular region, like the United States, for example, then that can probably weed out a lot of these workers that are in low-cost labor markets.

Question: Could you say anything more about the Klingon example? How did they get 1%? Was that just random chance or do you think you got lucky or unlucky and that the person actually knew Klingon?

Answer: I’d be amazed if they actually knew Klingon, but I actually think that they have a fairly small workforce, and if you saw the CAPTCHA examples that I presented, we also had one example number. So it’s possible that they saw a bulk number of these Klingon CAPTCHAs, and that same worker was like: “You know, I recognize that character now,” because we sent this 222 times. If that same worker has seen the same CAPTCHA over and over and has the example, he might remember the example built into the CAPTCHA. We don’t repeat digits in the same CAPTCHA, but it’s possible that they just learned. We taught them something, maybe.

Question: For the CAPTCHA that was based on dogs and cats – it seemed like the error rates were different when you deployed it and then when it was actually exposed as an API. Do you think that once they were exposing as an API, they actually go through and train their workers to solve these types of things?

Mr. Motoyama doing the CAPTCHA research Answer: Nowadays, I think PixProfit actually closed down the registration, but when you actually go through their 30 training examples, now they’re actually training examples, they’ll give you an Asirra CAPTCHA – you have to select these radio buttons, and they actually tell you whether you got it right or wrong. You’re not actually allowed to proceed past that CAPTCHA or not allowed to get admitted into the system until you’ve actually solved that CAPTCHA correctly.

Question: Do you think there’s room for arbitrage in this market, where you plug one guy into another like you were talking about? And sort of more generally, do you think there are economic ways that you can make these systems unprofitable for people running them?

Answer: In response to the second question, I guess it’s possible, because, for example, I saw this recently: I was getting CAPTCHA on the backend when I was solving CAPTCHAs, and they were just blank. And so, what would end up happening was that my account would get banned, because I can’t solve anything, right? But you’re also allowed to specify that the CAPTCHA has numbers in it, so you keep trying to submit this CAPTCHA and you keep getting it wrong. So that’s one way that you might maliciously affect these backend services. The first question – I suppose you could. Like ImageToText, maybe they’re selling some of Decaptcher’s or Antigate’s capabilities. I mean, that seems to make a lot of sense, right? I start up a website and all I do is charge you a little bit more, and then I just use one of these services to actually solve them. That makes a whole lot of sense.

Question: I was just wondering if when you signed up for these services to solve these CAPTCHAs, if you were actually getting paid; do these unscrupulous businesses remain true to their word in paying you?

Answer: I don’t think I was actually legally allowed to pull out the money from their accounts. I didn’t try. I’ve read online on many different forums that they’re legitimate and they do pay out the money.

Read previous: Understanding CAPTCHA-Solving Services in an Economic Context 5: Do CAPTCHAs Actually Work?

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