You would have probably come across CAPTCHAs while filling a registration form on a website. Those tangled image files or slightly distorted alphanumeric texts which have to be identified by you and typed on a text box before moving forward with the submission of a registration form are called CAPTCHAs. CAPTCHA basically stands for Completely Automated Public Turing test to tell Computers and Humans Apart.
These days CAPTCHAs have become ubiquitous. You encounter them while posting a comment on a blog. You encounter CAPTCHAs while applying for a job on a company’s website or for signing up on a website to avail some services. The main purpose for which the CAPTCHAs were invented was to stop spams from machines. To stop spams from machine CAPTCHA has to distinguish between a human and a computer or machine. Computer experts devised the method by utilising images of language. Images of language are randomly generated text and manipulated such that humans can read it but machines fail to identify them. Sometimes CAPTCHA offers to perform some task which are easier to perform by humans but almost impossible to perform by a machine. A human can easily read the text in image but a machine can only understand that it is an image file without identifying what this image is all about. CAPTCHAs also make use of an audio file so that dyslexic and visually impaired people can easily identify the CAPTCHA. Some CAPTCHAs ask to perform simple mathematical calculations like 7+3 = which are very common on blogs.
Protecting Fake Sign-up or Registrations
Company’s like Google, Yahoo and Microsoft offer free e-mail services to the public after signing up with them. A bot programme can sign up for thousands of users and thus register for that many e-mail accounts and that also in a few minutes. CAPTCHAs can prevent such bot programmes to attack such websites which provide free services.
Stopping Spams on Blogs
Bot programs can publish fake comments to improve the search engine rankings of the websites. By using CAPTCHAs machines can be stopped from commenting and only humans can comment on a blog without signing up.
Warding off Spams From E-mails
Spammers can crawl the web and identify e-mail addresses of the users and spam them with bogus e-mails. CAPTCHA is a way out which can prohibit such machine spammers to see the e-mail address by offering them to solve the CAPTCHA.
Online Opinion Polls
With the coming of Web 2.0 the internet has become more interactive with people. Online polls are becoming more and more popular with penetration of internet across the world growing faster and faster. We need to ensure in an online poll that votes are coming from genuine humans and not from any bot programme. CAPTCHA can ensure effectiveness of such online polls.
Safeguarding From Dictionary Attacks
Earlier the accounts of the user used to be locked after a series of unsuccessful logins. This practice gave attacker an opportunity to lock the account at his will. Now you can offer the user to solve for a CAPTCHA in order to prevent computer or machine to scan through entire space of passwords. Thus CAPTCHA prevents dictionary attacks on passwords.
Keep Webpages Unavailable for the Search Engines
Sometimes the need is like that you don’t want your webpage to be searched through a search engine bot. With the use of CAPTCHA you can prevent the webpage from the search engine bots.