"Captcha" is a method of blocking robots from commenting on websites and blogs. Something like 90% of all web comments are purported to be spam. Spammers use bits of software to crawl the web looking for comment forms and then post comments containing links to malware sites or porn or both. If there is no spam prevention or moderation process in place these links then appear on the victims site. If moderation is in place the comment will go to the moderator and will usually be stopped there, however there is still the risk that the user will click on a link and further damage will result. Captcha presents a human only readable block of text that has to be interpreted and typed into the comment form to verify that the comment is coming from a human. Given the number of sites using captcha now this represents quite a bit of untapped manpower.

reCaptcha is a brilliant idea that puts this work to good use in helping to digitize books. The process of digitizing books involves first scanning them to generate an electronic image. These images are human readable but not easy to store and can't be read by computer, for example for indexing or text to speech. OCR (optical character recognition) software is run against the image to translate the images of words into text that a computer can process and transmit. The OCR process is not perfect though and some words can't be translated. This is where reCaptcha from Carnegie Mellon University comes in, by presenting these images to humans to translate as part of the captcha process and thus transforming an irritating tasks performed by millions of people every day into thousands of man hours of useful work.

A downside from a web developers point of view is that recaptcha depends on the avialability of a third party service which may well not be maintained forever (what is these days), or will very likely be unavailable at times (this really depends on the infrastructure behind it and I don't know how resilient this is). Having said that, this is one of those simple ideas that strikes me as being pure genius. More info on recaptcha from here .

Average user rating