Google Captcha Dumps Distorted Text Images

Tired of reading those wavy words? Changes to Googles reCaptcha system -- which doubles as quality control for its book and newspaper scanning projects -- prioritize bot-busting puzzles based on numbers.

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Google is making changes to its reCaptcha system: distorted text images are out, while numbers and more-adaptive, puzzle-based authentication checks are in.
The change is necessary because text-only Captchas are no longer blocking a sufficient number of automated log-in attempts, according to Googles reCaptcha product manager, Vinay Shet. Over the last few years advances in artificial intelligence have reduced the gap between human and machine capabilities in deciphering distorted text, he said in a Friday
blog post
. Today, a successful Captcha solution needs to go beyond just relying on text distortions to separate man from machine.
Based on extensive user testing, Google thinks it can better separate real users from bots by using better risk analysis. This is based in part on watching what a supposed user is doing before, during and after the check, and serving up multiple puzzle-based checks. Although Shet didnt spell out exactly what these puzzles might look like, he did say that unlike humans, bots have a tough time with numbers.
[ Twitters new security measures can be a double-edged sword. Read
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. ]
Weve recently released an update that creates different classes of Captchas for different kinds of users. This multi-faceted approach allows us to determine whether a potential user is actually a human or not, and serve our legitimate users Captchas that most of them will find easy to solve, he said. Bots, on the other hand, will see Captchas that are considerably more difficult and designed to stop them from getting through.
The Captcha -- an acronym for Completely Automated Public Turing test to tell Computers and Humans Apart -- challenge-response technique was first developed at Carnegie Mellon University in 2000. The approach is designed to create a test that humans can pass, but computers cant. In theory, Captchas can be used for a variety of tasks, including preventing automated spam from appearing in blog comments, blocking automated spam-bot signup attempts for email services -- such as free Gmail accounts -- and safeguarding Web pages that site administrators dont want to be tracked by search bots.
In fact, Google
purchased reCaptcha
in 2009, in a bid to better block spammers who signed up for free accounts. The approach offered by reCaptcha was notable not just for presenting users with a Captcha phrase, but drawing those images from scans of books. That squares with Googles own Google Books and Google News Archive Search projects, which rely on optical character recognition (OCR) scans of printed source material, which arent 100% accurate. By designating scanned content for use with the reCaptcha system, however, Google killed two birds with one stone: creating a security check, while also tapping users to manually enter or verify scanned text for free.
In short order, Google also rolled out -- and still offers -- reCaptcha as a free anti-bot service that helps digitize books, and is available for use by any website. Answers to reCaptcha challenges are used to digitize textual documents, according to Googles reCaptcha overview. Its not easy, but through a sophisticated combination of multiple OCR programs, probabilistic language models, and most importantly the answers from millions of humans on the internet, reCaptcha is able to achieve over 99.5% transcription accuracy at the word level.
But no information security challenge-response system -- at least to date -- is perfect. Spam rings also have access to OCR tools, and have duly defeated many Captcha systems. Other criminal groups, echoing Googles crowd-sourced reCaptcha approach, have even tricked users into recording target sites Captcha phrases -- most sites have a finite pool of possibilities -- with the lure of
free porn
.
By adopting a more adaptive approach to verifying peoples identities via reCaptcha, Google has taken a page from Facebooks login verification system, which looks at a variety of factors when someone attempts to log into an account, including their geographic location, and whether theyre using a computer that Facebook has seen before. For unusual types of log-ins, Facebooks system can hit would-be users with an escalating series of security challenges.
Similarly,
RSAs Adaptive Authentication
system, which is used by about 70 of the countrys 100 biggest banks to verify their customers identity, assesses a number of risk factors before granting access. Based on different risk factors, furthermore, users can also be made to jump through more hoops before the system believes that they are who they say they are.
Its been a busy month for Captcha researchers. Earlier this month, a team of Carnegie Mellon researchers unveiled an
inkblot-based Captcha system
thats designed to defeat automated attacks.
This week, startup firm Vicarious claimed it has created an algorithm that can successfully defeat any text-based Captcha system, as well as defeat reCaptcha -- widely seen as the toughest Captcha system available -- 90% of the time,
New Scientist
reported. But Luis von Ahn, who was part of the Carnegie Mellon team that created Captchas, remains skeptical, saying hes counted 50 such Captcha-breaking claims since 2003. Its hard for me to be impressed since I see these every few months, he told
Forbes
.

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Google Captcha Dumps Distorted Text Images