What is CAPTCHA and How it Works?
CAPTCHA or Captcha (pronounced as
cap-ch-uh) which stands for “Completely Automated Public Turing test to
tell Computers and Humans Apart” is a type of
challenge-response
test to ensure that the response is only generated by humans and not by
a computer. In simple words, CAPTCHA is the word verification test that
you will come across the end of a sign-up form while signing up for
Gmail or Yahoo account. The following image shows the typical samples of
CAPTCHA.
Almost every Internet user will have an
experience of CAPTCHA in their daily Internet usage, but only a few
are aware of what it is and why they are used. So in this post you will
find a detailed information on how CAPTCHA works and why they are used.
What Purpose does CAPTCHA Exactly Serve?
CAPTCPA is mainly used to prevent
automated software (bots) from performing actions on behalf of actual
humans. For example while signing up for a new email account, you will
come across a CAPTCHA at the end of the sign-up form so as to ensure
that the form is filled out only by a legitimate human and not by any of
the automated software or a computer bot. The main goal of CAPTCHA is
to put forth a test which is simple and straight forward for any human
to answer but for a computer, it is almost impossible to solve.
What is the Need to Create a Test that Can Tell Computers and Humans Apart?
For many the CAPTCHA may seem to be
silly and annoying, but in fact it has the ability to protect systems
from malicious attacks where people try to game the
system. Attackers can make use of automated softwares to generate a huge
quantity of requests thereby causing a high load on the target server
which would degrade the quality of service of a given system, whether
due to abuse or resource expenditure. This can affect millions of
legitimate users and their requests. CAPTCHAs can be deployed to protect
systems that are vulnerable to email spam, such as the services from
Gmail, Yahoo and Hotmail.
Who Uses CAPTCHA?
CAPTCHAs are mainly used by websites
that offer services like online polls and registration forms. For
example, Web-based email services like Gmail, Yahoo and Hotmail offer
free email accounts for their users. However upon each sign-up process,
CAPTCHAs are used to prevent spammers from using a bot to generate
hundreds of spam mail accounts.
Designing a CAPTCHA System
CAPTCHAs are designed on the fact that
computers lack the ability that human beings have when it comes to
processing visual data. It is more easily possible for humans to look at
an image and pick out the patterns than a computer. This is because
computers lack the real intelligence that humans have by default.
CAPTCHAs are implemented by presenting users with an image which
contains distorted or randomly stretched characters which only humans
should be able to identify. Sometimes characters are striked out or
presented with a noisy background to make it even more harder for
computers to figure out the patterns.
Most, but not all, CAPTCHAs rely on a
visual test. Some Websites implement a totally different CAPTCHA
system to tell humans and computers apart. For example, a user is
presented with 4 images in which 3 contains picture of animals and one
contain a flower. The user is asked to select only those images which
contain animals in them. This Turing test can easily be solved by any
human, but almost impossible for a computer.
Breaking the CAPTCHA
The challenge in breaking the CAPTCHA
lies in real hard task of teaching a computer how to process information
in a way similar to how humans think. Algorithms with artificial
intelligence (AI) will have to be designed in order to make the computer
think like humans when it comes to recognizing the patterns in images.
However there is no universal algorithm that could pass through and
break any CAPTCHA system and hence each CAPTCHA algorithm must have to
be tackled individually. It might not work 100 percent of the time, but
it can work often enough to be worthwhile to spammers.
EnjOy.. =))
MamoOn..
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