CAPTCHA is one of the most popular ways to stop Web robots from posting links in the comment section of your blog or submitting false entries in forms on your Web site. You've probably encountered it on various Web sites when entering information. You have to type the distorted letters you see in a box before submitting your information.
If you're thinking about using CAPTCHA on your Web site or blog to prevent comment spam and false accounts generated by robots, you might be surprised to find out that if you follow through, you'll be helping create digital archives of publications printed before the dawn of the digital age.
Developed by researchers at Carnegie Mellon, the system is based mostly on open software, and a version of it is available for free download.
Interestingly, the developers have figured out a way to put all the effort involved in solving these little puzzles to good use. When you enter the words, you're helping computers read an unrecognizable word from a scanned image.
To address the problem of typos, the software compares your answer to that of other people’s before it is accepted as the correct word. Each CAPTCHA also includes a control word that you must enter correctly (to prove that you're a human, not a robot).
The downside to screening entries this way is that you may inadvertently prevent people with disabilities such as blindness, low vision or dyslexia from accessing your resources. If you decide to use CAPTCHA for your Web site, make sure you provide alternative means of verification so you don't exclude some humans in addition to robots.