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Questioning CAPTCHA Usability

Since the first interactive form was put on the Internet, bot writers have been writing programs to automatically exploit them. To prevent this, programmers began putting those screwy images of warped letters and numbers on the screen and asking you to key them in. This is known as a turing test, a sort of intelligence test to tell a computer and a human apart.
This works fairly well for those of us who have our eyesight, but what about the visually impaired? Yesterday I sent you to get a $40 coupon toward a digital converter box. If you filled out the coupon, you were challenged with a CAPTCHA code. For the visually impaired, you would click on the speaker icon and hear a code for you to type in like this one garbledCaptcha.mp3.
I listen to that sequence and it just sounds terrible. Perhaps the problem is that I have all my senses, so my hearing is not heightened to make up for vision. I guess that the same exploits that attempt to decode CAPTCHA images are also used to parse these audio files, thus the poor quality and background noise. Still, I don’t think I would’ve gotten this one right.
In the case of the digital tv site, they provided a link to download a paper application to fill out. The visually impaired person would still no doubt need help in filling it out, but at least there were other options presented. Many sites don’t offer that capability (think of places like Ticketmaster where the only other option is slow service over the telephone).
Defeating the automated bots is a necessary task, but I think that the evolution needs to continue. Perhaps this would be a good route for a PhD thesis…

One Comment Post a comment
  1. Hi Mike,
    It’s quite true that despite the minor enhancements to CAPTCHA, a huge usability problem still exists. I would be interested to hear your feedback to an alternative solution recently developed that is much easier on users and is effective against bots. It can be found at It’s offered at NO charge as a web service if you want to use it on your own site.

    January 26, 2009

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