cAPTCHA – SEO WIKI
CAPTCHA is an acronym for C.a.p.t.c.h.a. (Completely Automated Public Turing test to tell Computers and Humans Apart).
CAPTCHA is a security code that a user must enter to gain access to the desired information or service. This code is designed to distinguish between automated bots and people, and reduce the number of automatic registrations and spam. Most often it is used on forums, sites with registration, in online services and so on.
The concept of SEO and CAPTCHA is not strongly related, however, in search engines very often with a high frequency of inputting requests, CAPTCHA can appear to eliminate the big load on the server from automatic programs that parse statistics and keywords.
There are a number of methods to circumvent captcha, the simplest of which is the use of proxy servers.