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Summary: You've probably seen Captcha's and not even realized it. Captcha's are used frequently to make sure that systems aren't gamed or spammed by machines. It'd been quite a while since I received your newsletter and it was then that I realized that the reason for this was that my GMail through Outlook 2003 was not working! I browsed over to Gmail.com and sure enough, the mail was there! Someone pointed out that I should go to UnlockCaptcha. And I did, that's when my Gmail POP started working . I am curious what is a "Captcha"? It's a bit of computer science geekery that you probably have interacted with many times before. Captcha is an acronym for "completely automated public Turing test to tell computers and humans apart." It's even trademarked by Carnegie Mellon University. Here's why that's important... • One of the oldest problems in computer science is to build a computer or software that mimics "thinking" like a human, and does it so well that you couldn't tell the difference. You could ask it a series of questions, and you wouldn't be able to tell whether the responses came from a real human or a computer. That's referred to as a form of "Turing test", after the computer scientist Alan Turing. A Captcha is a kind of "reverse Turing test". In essence it's a way of proving that you're human. You know those images with slightly scrambled letters, where you're supposed to type in what you see? That is a Captcha. Deciphering those letters is currently beyond the ability of contemporary mass market computers and software. Since you and I can typically make out what those letters are, and then type them in correctly, we must not be computers. We've proven that we're human. "You know those images with slightly scrambled letters,
where you're supposed to type in what you see? That is a Captcha."
Why do we care? As with so many things these days, it mostly comes back to spam. Here's one example: without a Captcha, it would be easy to write a computer program to open hundreds or thousands of Hotmail accounts, and start spamming from them. Once the accounts are blocked, the program can just as easily start creating thousands more. It really would be as easy as it sounds for a reasonably competent programmer. However, at some point along the account creation process, Hotmail presents a Captcha, saying in effect "prove to me that you are not a computer, and I'll let you create this account". The computer program is stopped dead in its tracks. I suspect that you actually experienced something similar. GMail apparently tries to prevent similar abuse by preventing you from accessing your POP3 mail "too often" (whatever that means). Apparently you tripped the limit, and GMail locked out your POP3 access. In order to restore that access you had to - you guessed it! - prove that you're human. That "UnlockCaptcha" page has two things on it: a place for you to enter your account name and password, and the Captcha: a bunch of distorted text for you to type in. Captcha's have one big drawback: they assume you can see. Blind computer users, of which there are many, can by definition not complete a visually oriented Captcha. There are alternative types of Captchas - some using images (match the word to the picture), or even simple math (what's the answer when you add these two numbers) that can, sometimes, work better. Alternatively some sites include a link to an completely different verification mechanism for those with vision problems. The Google page you mentioned includes an icon that, when clicked on, plays an audio version of the Captcha. (Sadly, it requires plugins and ActiveX controls, so it's still not particularly seamless, but it's better than nothing at all.) The future of Captcha is also interesting. There's no doubt that image processing software and computers themselves will become more powerful and eventually will be able to automatically decipher today's Captcha images. What than? Related:
Article 10430 | Posted June 19, 2006 |
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I saw an interesting Captcha the other day. Instead of a picture it had an easy to answer question. Something like "Which is not a tree? with six possible answers. The wrong answer was "2x4". Since it was text it could easily be used by a screen reader. It would be interesting to know how easy it would be to beat.
Posted by: Dan Ullman at June 19, 2006 02:18 PMI didn't know that these things had a specific name. I suppose "captcha" sounds better than "gotcha". :-)
I encounted one the other day (I think it was eBay's "contact the seller" link) which included a "hear the code" link next to the picture. I guess they're getting enough flak from people who can't see the pictures to enter the code.
Posted by: Ken at June 20, 2006 07:56 AMOf course, the way spammers get around CAPTCHA technology is to proxy the CAPTCHA. They put up a site offering something like free photos of adult entertainers, then require the user to run through a CAPTCHA to get in. Thing is, it's your CAPTCHA, and when the user runs through it, the answer is sent to your site so the spammer can spam you.
The real trick would be a CAPTCHA that could not be proxied.
Posted by: Greg Bulmash at June 21, 2006 10:34 AMThanks Leo, that kinda "CAPTCHAD" my imagination.
Posted by: Danny Garcia at June 22, 2006 07:52 AMhaving to go to captcha every time I change rooms is a pain. Can I get around this?
Posted by: shirley warbington at September 10, 2007 03:16 AM