Diligent teaspoons: how to put Captchas to work

Regenerative braking is the process by which a car like the Toyota Prius can simultaneously slow down your car and turn some of your kinetic energy into electricity. The basic insight is this: a moving car is lovely energy source, waiting to be harvested. When you step on the brakes, as eventually you must, your ordinary old pre-Prius can only convert that energy into brake heat. But if you employ some clever electromagnetic torque, you can recapture that same energy, energy that otherwise goes pouring down the entropy hole in God’s great plenty every day.

Recapturing energy otherwise lost is the idea behind the reCaptcha, as I learned from this post to the O’Reilly Radar site. To understand the reCaptcha, you first have to understand the Captcha. Captchas were invented by Louis von Ahn and others at CMU as a way of stopping naughty computer programs from masquerading as humans (Captcha is the improbable acronym for Completely Automated Turing Test To Tell Computers and Humans Apart). When, for example, Hotmail gives you a free account, they want to make sure you’re a real person. The way they do this by making you read some blurry smeared text like this.


Von Ahn’s latest brainstorm was to realize that “in aggregate these little puzzles consume more than 150,000 hours of work each day.” Like cars in motion, that’s an energy source that’s crying out to be harvested. So his new reCaptchas give you two words to decode. For one of these, he already knows the answer. But the other one is from a book scan that a computer is having a hard time reading. By deciphering the text, you’re actually helping to digitize books from the Internet Archive.

Harvesting energy one teaspoon at a time is theme that fascinates me, because it seems to promise something for nothing. Of course it’s really just a matter of spotting untapped energy sources and putting the right machine in place to capture it. Here, for example, is a New Scientist article about harvesting heat energy: Mini heat harvesters could be new energy source. This technique sometimes goes under the heading of energy scavenging, as studied by Rajeevan Amirtharajah’s group at UC Davis. “Energy scavenging” is a marvelous phrase. I think that’s what my son does to me.