If you frequently surf the internet sometimes you will find an article as above if it will register after completing the registration form, it is called Captcha. What is Captcha?
Captcha (called cap-ch-uh) or CAPTCHA is Completely Automated Public Turing test to tell Computers and Humans Apart is a challenge-response test that is intended to ensure that the respondent is only carried by humans and not by computers.
Here are some of the functions of Captcha:
1. Prevent comment spam generally Own web / blog / etc do not just want komment its look nice in appearance, quantity but of quality.
2. Preventing Spam Bot Bot or robots can not read the captcha, since its programming string string is fixed. capthca which may not at any time change can be read unless it comes from engine bot Blog itself.
3. Prevent Flood Flood is mangirimkan data over and over again.
4. Protect Registration Email / User (special webmail)
Figure letter turmoil called CAPTCHA, this is one application of the method Turing Test which was initiated by Alan Turing in 1950. Point to ensure that the form filler is actually a man. The computer program will have difficulty in deciphering the letters are twisted or stacked while the man is still in a (somewhat) easier to read. Before there CAPTCHA, spammers / hackers can create a program to automatically fill in a form like an email signup for free, so that it will acquire thousands of email addresses with ease and then misused or to alter the results of an online poll, someone could just make a simple program to fill the poll with the same answer as many thousands or even millions of times. As a result, the poll was of course to be invalid.