A computer screen saying 'I'm not a robot'

CAPTCHAs are hard for computers to solve, but easy for humans

Image: © Hruts

By Mike McRae

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Casper, age 9, asks
How do ‘I am not a robot’ quizzes work?

If you’ve provided your name and details on a website, you might be asked to click on a box to prove you’re not a ‘robot’. Of course, it’s not asking if you’re made of metal and circuits – it’s asking you to prove you’re not a program.

Some programs are designed to quickly create numerous fake profiles for social media. Others will swamp a website to overload it, forcing it to shut down.

Protective programs called ‘Completely Automated Public Turing tests to tell Computers and Humans Apart’ – or CAPTCHAs – ask users to do something we know computers can’t yet do very well. In some cases, this involves reading looping letters, or choosing photographs with a specific item in them, such as a car or bridge.

But computers are getting better at doing these things. A few years ago, Google came up with something called reCAPTCHA, which requires you to just click a box.

By comparing your computer’s address with things like your browsing history and how you move your mouse, reCAPTCHA can judge whether a human clicked the box or a program checked it!

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3 responses

  1. Alan Reynolds Avatar
    Alan Reynolds

    The odd thing about clicking the photos is the specificity of the message.
    Select all traffic lights.
    Does this include the structure or just the lights?
    I really feel that you have to second guess these people.

    1. David Avatar

      Your answer is judged based on what other people have also answered. So if most people would include the structure, you probably have to include the structure. The system doesn’t have a real correct answer.

      Occasionally, it’ll accept a clearly wrong answer – in that case, you’re probably one of the first people to answer that question for that image. It’s still learning what humans thing the right answer is!

  2. David Avatar

    Thank you to Casper for asking. In spite of the strong hints of its all capitals format, it hadn’t occurred to me that CAPTCHA was yet another acronym. A trivia night question there..

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