Google offers top tip to help beat bots

By asking visitors to find the top of a randomly rotated image, it hopes to keep bots out of Web services such as Gmail

Google has put a new spin on the CAPTCHA, a way of helping Web sites distinguish between human visitors and bots: It wants people to tell it which way is up in a series of randomly rotated images, a task that humans find easy and computers difficult.

When spammers started using software to automatically create thousands of Web-mail accounts on services such as Hotmail and Gmail from which to send their spam, the Web-mail operators turned to the CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) to weed out automated applicants.

A typical CAPTCHA asks the visitor to look at an image containing a series of distorted letters and numbers set against a busy background, and to type in the sequence of characters they see. The idea is that a human can easily recognize the shapes of the letters, while a computer program will find it difficult to do so.

However, OCR (optical character recognition) software has become more sophisticated, forcing CAPTCHA developers to make their challenges so unreadable that many humans have trouble too.

Google's answer is to show visitors randomly rotated images and ask them which way is up.

However, while the images will be randomly rotated, they will be carefully selected. First, Google will exclude images for which its own computers can readily identify the top, such as photographs showing landscapes with blue sky (easily detected), text (easily recognized) or portraits of people (there are many facial recognition applications on the market).

Then, it will screen out images that humans find too difficult to orient (for example, abstract art, or overhead views, that don't have a readily identifiable top) by conducting a sort of opinion poll.

That poll is the key to the process, as it allows Google to create a pool of appropriate images for which people agree on the correct orientation.

By challenging visitors with a series of images for which it knows the orientation, and one for which it doesn't, Google can screen out the bots and steadily accumulate statistics about the unknown image: If visitors tend to agree which way is up, it's appropriate for inclusion, and if they disagree, the image may be too difficult.

Google employees Rich Gossweiler, Maryam Kamvar and Shumeet Baluja describe the image selection process in a paper, "What's Up CAPTCHA?" that they will present next Thursday at the WWW 2009 conference in Madrid.

They are not the first to consider using photographs in CAPTCHAs. For instance, in August 2007, Microsoft asked visitors to distinguish between cats and dogs in an attempt to stop the spam bots.

Recent advances in face recognition software, though, may have rendered that approach obsolete: Apple's iPhoto application can already identify cats' faces, but has trouble with dogs, suggesting that software capable of deliberately distinguishing between the two may not be far off.

However clever Google gets, though, the spammers may be cleverer. There is evidence that they are employing humans to crack the current crop of CAPTCHAs, presenting the challenges as a game, paying people in low-income countries to solve them - or reframing the CAPTCHAs as a way to gain access to porn sites. Against that kind of attack, there is little that Google can do.

Join the newsletter!

Error: Please check your email address.
Rocket to Success - Your 10 Tips for Smarter ERP System Selection

Tags spamGoogleantispamcaptcha

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Peter Sayer

IDG News Service
Show Comments

Cool Tech

Breitling Superocean Heritage Chronographe 44

Learn more >

SanDisk MicroSDXC™ for Nintendo® Switch™

Learn more >

Toys for Boys

Family Friendly

Panasonic 4K UHD Blu-Ray Player and Full HD Recorder with Netflix - UBT1GL-K

Learn more >

Stocking Stuffer

Razer DeathAdder Expert Ergonomic Gaming Mouse

Learn more >

Christmas Gift Guide

Click for more ›

Most Popular Reviews

Latest Articles

Resources

PCW Evaluation Team

Walid Mikhael

Brother QL-820NWB Professional Label Printer

It’s easy to set up, it’s compact and quiet when printing and to top if off, the print quality is excellent. This is hands down the best printer I’ve used for printing labels.

Ben Ramsden

Sharp PN-40TC1 Huddle Board

Brainstorming, innovation, problem solving, and negotiation have all become much more productive and valuable if people can easily collaborate in real time with minimal friction.

Sarah Ieroianni

Brother QL-820NWB Professional Label Printer

The print quality also does not disappoint, it’s clear, bold, doesn’t smudge and the text is perfectly sized.

Ratchada Dunn

Sharp PN-40TC1 Huddle Board

The Huddle Board’s built in program; Sharp Touch Viewing software allows us to easily manipulate and edit our documents (jpegs and PDFs) all at the same time on the dashboard.

George Khoury

Sharp PN-40TC1 Huddle Board

The biggest perks for me would be that it comes with easy to use and comprehensive programs that make the collaboration process a whole lot more intuitive and organic

David Coyle

Brother PocketJet PJ-773 A4 Portable Thermal Printer

I rate the printer as a 5 out of 5 stars as it has been able to fit seamlessly into my busy and mobile lifestyle.

Featured Content

Product Launch Showcase

Latest Jobs

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?