The Story of Captcha and its Variants

Coined by a creatively influential and inventive team of Carnegie Mellon professors comprising Luis von Ahn, Nicholas J. Hopper, John Langford and Manuel Blum, CAPTCHA stands for Completely Automated Public Turing Test to tell Computers and Humans Apart. Captchas was first put to use in the early 2000 by the reputed search engine giants Alta Vista and Yahoo. Touted as one of the most powerful weapons that helps fight web spams and dubious chat bots, Captcha is a befitting solution to prevent fraud URL submissions as well.

Turing Test

Turing test is a test named after the father of modern computer science- Alan Turing. Turing test is all about identifying the machines that exhibit intelligent behavior. In other words, if a machine passes the Turing test, it is said to be ‘intelligent’. Turing test necessitates that a machine should converse with judges through a dedicated text interface. If the judges fail to identify and affirm if they are chatting with a machine or man, the machine is said to have passed the Turing test. Captcha has undergone several progressive transformations and has undoubtedly evolved over a period of time.

Types of Captcha

Here are the various types of Captcha −

  • Text-based Captcha − This is the most common type of Captcha where text is usually presented in a distorted fashion. Sometimes, text is twirled, twisted in various possible directions thereby making it difficult for automated chat bots to decipher the text. The text displayed in the Captcha box is striked out and scrambled. Humans find it easy and trivial to decipher the text.
  • ReCAPTCHA − ReCAPTCHA is in fact the name of one of the popular Captcha companies. ReCAPTCHA has become so famous for its Captchas that the entire internet fraternity has rechristened its distorted text images as ‘ReCAPTCHAs.’ Touted as the most reliable variant of Captcha, ReCAPTCHA is usually a wholesome mix of distorted text and some audio. If you are unable to decipher the text, you can make use of the audio option and then type the text in the space provided. More often than not, ReCAPTCHAs are hard to solve and hence, many users end up clicking “recaptcha” option thereby hedging their bets on new texts.

  • Mathematical Captcha − You do not need to be a Srinivasa Ramanujan to solve Mathematical Captchas. That being said, the difficulty of cracking the Mathematical Captchas is increasing day by day. Gone are the days when Mathematical Captchas used to be simple numerical calculations such as 1+3, 4-1 etc., Mathematical Captchas are now replete with differentiation and integration functions. On a lighter note, even less knowledgeable humans fail to exhibit intelligent behavior in such cases. By the way, Mathematical Captchas are also associated with twisted text and an audio option. If you fail to decipher the text, you can count on ‘audio’ option or request for another one.
  • Image-based Captcha − In Image-based Captchas, several pictures are juxtaposed and simple actions such as Click all the images of animals or Click all the images of cats are to be performed by the user. The fact that automated chat bots find it increasingly difficult to distinguish one kind of image from another kind works in favor of Image-based Captchas. Sometimes, Image-based Captchas are tough nuts to crack as questions such as Click all the images of cats will be asked where apart from normal sized domestic cats, big sized feline images will also be displayed. To assist humans in such cases, a few hints such as – identification of cats requires not more than 7 clicks etc. are provided.
  • Logic-based Captchas − Logic-based Captchas have become the latest fad. Humans need to use their intelligence and of course, their common sense to answer the Captchas correctly. Though the questions may seem trivial, automated chat bots find it extremely difficult to crack Logic-based Captchas. A few examples include:
  • 3D Captchas − 3D Captchas are eye-straining and nerve-wracking. Leave apart automated chat bots and other malicious programs, even humans find 3D Captchas difficult. 3D Captchas are also called ‘Super Captchas’ for their 3D images and words.
  • Commercial Captchas − Also called as ‘Ad-Injected Captchas’, Commercial captchas in-fact help website owners earn some extra money every time the ad(s) is (are) clicked. The distorted text should be deciphered and entered correctly in the space provided and more often than not, the space to enter the text is provided just beneath the displayed ad. There are two benefits- You make some decent revenue and at the same time, brand promotion and brand recognition become all the more impactful. Of-course, web spam attacks are also obviated.

Well, Captchas are reliable and secure. However, sophisticated technologies can be used to break few kinds of Captcha (if not all). That being said, it is the responsibility of the entire web fraternity to distance itself from spam attacks and cyber-thefts.

karthikeya Boyini
karthikeya Boyini

I love programming (: That's all I know

Updated on: 17-Jan-2020


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