What is CAPTCHA?
CAPTCHA stands for *C*ompletely *A*utomated *P*ublic *T*uring test to tell *C*omputers and *H*umans *A*part. Basically it means those pictures with wavy letters that you have to type in before being allowed to sign up for a mailing list or other service. They are an attempt to prevent “spamming” or automatic signups by programs. Apparently there are some audio versions as well.
- PHP CAPTCHA Class
reCAPTCHA is a very intriguing project that uses CAPTCHA authentication to help correct OCRA software and digitize books for the internet archive. Fiat Lux!
Techniques and Arguments against CAPTCHA