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MASSIVE-SCALE ONLINE COLLABORATION Luis von Ahn - April 2011 Louis von Ahn is an associate professor of Computer Science at Carnegie Mellon University, and he’s at the forefront of the crowdsourcing craze, building systems that combine humans and computers to solve large-scale problems that neither can solve alone. His work takes advantage of the evergrowing Web-connected population to acheive collaboration in unprecedented numbers. His projects aim to leverage the crowd for human good. His company reCAPTCHA, sold to Google in 2009, digitizes human knowledge (books), one word at a time. His new project is Duolingo, which aims to get 100 million people translating the Web in every major language. 0:00 0:13 0:39 1:13 1:35 2:07 “ How many of you had to fill out some sort of web form where you’ve been asked to read a distorted sequence of characters like this? How many of you found it really, really annoying? Okay, outstanding. So I invented that. (Laughter) Or I was one of the people who did it. That thing is called a CAPTCHA. And the reason it is there is to make sure you, the entity filling out the form, are actually a human and not some sort of computer program that was written to submit the form millions and millions of times. The reason it works is because humans, at least non-visually-impaired humans, have no trouble reading these distorted squiggly characters, whereas computer programs simply can’t do it as well yet. So for example, in the case of Ticketmaster, the reason you have to type these distorted characters is to prevent scalpers from writing a program that can buy millions of tickets, two at a time. CAPTCHAs are used all over the Internet. And since they’re used so often, a lot of times the precise sequence of random characters that is shown to the user is not so fortunate. So this is an example from the Yahoo registration page. The random characters that happened to be shown to the user were W, A, I, T, which, of course, spell a word. But the best part is the message that the Yahoo help desk got about 20 minutes later: “Help! I’ve been waiting for over 20 minutes, and nothing happens.” (Laughter) This person thought they needed to wait. CAPTCHA Project is something that we did here at Carnegie Melllon over 10 years ago, and it’s been used everywhere. Let me now tell you about a project that we did a few years later, which is sort of the next evolution of CAPTCHA. This is a project that we call reCAPTCHA, which is something that we started here at Carnegie Mellon, then we turned it into a startup company. And then about a year and a half ago, Google actually acquired this company. So this project started from the following realization: It turns out that approximately 200 million CAPTCHAs are typed everyday by people around the world. When I first heard this, I was quite proud of myself. I thought, look at the impact that my research has had. But then I started feeling bad. See here’s the thing, each time you type a CAPTCHA, essentially you waste 10 seconds of your time. And if you multiply that by 200 million, you get that humanity as a whole is wasting about 500,000 hours every day typing these annoying CAPTCHAs. So then I started feeling bad. (Laughter) And then I started thinking, well, of course, we can’t just get rid of CAPTCHAs, because the security of the Web sort of depends on them. But then I started thinking, is there any way we can use this effort for something that is good for humanity? So see, here’s the thing. While you’re typing a CAPTCHA, during those 10 seconds, your brain is doing something amazing. Your brain is doing something that computers cannot yet do. So can we get you to do useful work for those 10 seconds? Another way of putting it is, is there some humongous problem that we cannot yet get computers
to solve, yet we can split into tiny 10-second chunks such that each time somebody solves a CAPTCHA they solve a little bit of this problem? And the answer to that is “yes,” and this is what we’re doing now. 2:41 3:07 3:90 4:31 5:17 6:05 So what you may not know is that nowadays while you’re typing a CAPTCHA, not only are you authenticating yourself as a human, but in addition you’re actually helping us to digitize books. So let me explain how this works. So there’s a lot of projects out there trying to digitize books. Google has one. The Internet Archive has one. Amazon, now with the Kindle, is trying to digitize books. Basically the way this works is you start with an old book. You’ve seen those things, right? Like a book? (Laughter) So you start with a book, and then you scan it. Now scanning a book is like taking a digital photograph of every page of the book. It gives you an image for every page of the book. This is an image with text for every page of the book. The next step in the process is that the computer needs to be able to decipher all of the words in this image. That’s using a technology called OCR, for optical character recognition, which takes a picture of text and tries to figure out what text is in there. Now the problem is that OCR is not perfect. Especially for older books where the ink has faded and the pages have turned yellow, OCR cannot recognize a lot of the words. For example, for things that were written more than 50 years ago, the computer cannot recognize about 30 percent of the words. So what we’re doing now is we’re taking all of the words that the computer cannot recognize and we’re getting people to read them for us while they’re typing a CAPTCHA on the Internet. So the next time you type a CAPTCHA, these words that you’re typing are actually words that are coming from books that are being digitized that the computer could not recognize. And now the reason we have two words nowadays instead of one is because, you see, one of the words is a word that the system just got out of a book, it didn’t know what it was, and it’s going to present it to you. But since it doesn’t know the answer for it, it cannot grade it for you. So what we do is we give you another word, one for which the system does know the answer. We don’t tell you which one’s which, and we say, please type both. And if you type the correct word for the one for which the system already knows the answer, it assumes you are human, and it also gets some confidence that you typed the other word correctly. And if we repeat this process to like 10 different people and all of them agree on what the new word is, then we get one more word digitized accurately. So this is how the system works. And basically, since we released it about three or four years ago, a lot of websites have started switching from the old CAPTCHA where people wasted their time to the new CAPTCHA where people are helping to digitize books. So for example, Ticketmaster. So every time you buy tickets on Ticketmaster, you help to digitize a book. Facebook: Every time you add a friend or poke somebody, you help to digitize a book. Twitter and about 350,000 other sites are all using reCAPTCHA. And in fact, the number of sites that are using reCAPTCHA is so high that the number of words that we’re digitizing per day is really, really large. It’s about 100 million a day, which is the equivalent of about two and a half million books a year. And this is all being done one word at a time by just people typing CAPTCHAs on the Internet. (Applause) Now of course, since we’re doing so many words per day, funny things can happen. And this is especially true because now we’re giving people two randomly chosen English words next to each other. For example, we presented this word. It’s the word “Christians”; there’s nothing wrong with it. But if you present it along with another randomly chosen word, bad things can happen. So we get this: “bad christians”. But it’s even worse, because the particular website where we showed this actually happened to be called The Embassy of the Kingdom of God. (Laughter) Oops. (Laughter)Here’s another really bad one: “damn liberal” on JohnEdwards.com. (Laughter) So we keep on insulting people left and right everyday. Now, of course, we’re not just insulting people. See here’s the thing, since we’re presenting two randomly chosen words, interesting things can happen. So this actually has given rise to a really big Internet meme that tens of thousands of people have participated in, which is called CAPTCHA art. I’m sure some of you have heard about it. Here’s how it works. Imagine you’re using the Internet and you see a CAPTCHA that you think is somewhat peculiar, like “invisible toaster”. Then what you’re supposed to do is you take a screen shot of it and you draw something that is related to it. MASSIVE-SCALE ONLINE COLLABORATION 5
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