CAPTCHA The Moment

Do you know what CAPTCHAs are? They’re those ubiquitous word recognition challenges that web services use to make sure you’re a human being. Invented by researchers at Carnegie Mellon University in 2000, CAPTCHA stands for “Completely Automated Public Turing test to tell Computers and Humans Apart”. Ticketmaster, for example, uses CAPTCHAs to prevent automated scalper-bots from buying up all the tickets to popular concerts.

It’s a pretty cool idea – it exploits the fact that computer software, advanced though it may be, has a difficult time doing something we humans take for granted: recognizing messy, ambiguously constructed text. The downside, of course, is that in order to stay a step ahead of the bad guys, over time CAPTCHAs have gotten harder to recognize by humans. Take this one, for example, with which I was just presented when signing up for a new service:


I can tell the second word is “urnice” but am I supposed to recognize that first word? As far as I can tell, it’s an ink stain.

Perhaps now might be a good time to admit that I impose CAPTCHAs on people leaving comments on this blog. I do so reluctantly to thwart a high level of spam comments, however, it annoys me to no end that in order to deter spammers, I have to make life more difficult for legitimate visitors. Recently I added support for integrated Facebook comments, which seems like a nice way to solve both problems (it’s convenient and largely spam-proof), the only downside being that I’m aiding and abetting Facebook’s inexorable march toward world domination.

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