reCAPTCHA is a free service that shows anti-bot distorted texts and lets the user read and enter it into a text box. This prevents bots and scripts from accessing certain areas of a site and enhances security. Most of us have known this service for only the above purpose but reCAPTCHA has another goal which happens to be more interesting one.
reCAPTCHA helps converting old books, news papers and texts into digital text. Typical OCRs are unable to read the older books with blurred ink, grained papers and even partially torn and withered pages. OCR software are confident about some words that they convert and for so many words, these software are doubtful. All these words are used as online CAPTCHAs on different sites by reCAPTCHA and human users read them and tell the right text to the service. This reduces or even eliminates the need of human intervention during the digitization process. Click here to see how reCAPTCHA works.
reCAPTCHA has been doing very interesting work and recently Google has acquired reCAPTCHA. This will not only help Google improve things with their CAPTCHA but also will boost digitization for google books and news etc.