nothing useful ,, only useful possible if u r n engineering student in india.

1. UE6858
“CAPTCHAS”
“CAPTCHAS”
Submitted in fulfillment of Seminar required for the
Bachelor of Engineering (B.E)
In
Information Technology
By
Sachin Narang
UE6858, 8th Semester
Panjab University
Under the Supervision
Of
Ms. Roopali Garg
Associate Professor, UIET
UE6858 Page 1

2. UE6858
“CAPTCHAS”
Contents
S.No Topic Page No.
1 Cover Page 1
2 Contents 2
3 Acknowledgment 3
4 Declaration 4
5 Certificate 5
4 Introduction 6
5 Why use CAPTCHAS 7
6 Definitions 8
7 Types of CAPTCHAS 9
8 Major Areas Of Applications 11
9 ReCAPTCHA 14
10 Breaking of CAPTCHAS 16
11 New Proposed Approaches 17
12 Conclusion 19
13 Bibliography 20
Acknowledgement
UE6858 Page 2

3. UE6858
“CAPTCHAS”
This is to thank all those who supported and helped me throughout the
commencement of this seminar report. I would like to thank specially my
teacher in-charge, Ms. Roopali Garg for her continuous guidance. I would
also like to thank my friends for their encouragement. Also, each time they
found a mistake and suggested a correction and led this seminar to
perfection.
Sachin Narang
B.E, I.T, UE6858
U.I.E.T
Declaration
UE6858 Page 3

4. UE6858
“CAPTCHAS”
I hereby declare that the work which is being presented in this seminar
report on ‘CAPTCHAS’ submitted at U.I.E.T., Panjab University is an
authentic work presented by Mr. Sachin Narang (UE6858) of B.E. (I.T.) 8th
semester under the supervision of Ms. Roopali Garg.
Sachin Narang
B.E, I.T, UE6858
U.I.E.T
Certificate
UE6858 Page 4

5. UE6858
“CAPTCHAS”
This is to certify that Mr. Sachin Narang, UE6858 , B.E. (I.T.) 8th Semester
have completed seminar report, in accordance with the requirement for
qualifying 8th semester, on CAPTCHAS under the guidance of Ms. Roopali
Garg.
Roopali Garg
Associate Professor
(Teacher In-Charge)
Introduction
UE6858 Page 5

6. UE6858
“CAPTCHAS”
Use of INTERNET has remarkably increased Globally in the
past 10-12 years and so is the need of the Security over it.
Marketing and Advertisement over INTERNET has seen
companies like GOOGLE being made, which at the moment
is traded at 181 billion USD ie. Almost twice of General
Motors, McDonalds combined.
Well this presentation is about Security achieved over
Internet using CAPTCHAS. CAPTCHAS are basically
software programs which act as a test to any user over
internet that the person (user) is a human or another
machine. This concept is used by all the big companies
over internet Google, yahoo or facebook (name any).So
what are these CAPTCHAS? And what are their possible
applications? This is what we cover in our presentation.
UE6858 Page 6

7. UE6858
“CAPTCHAS”
Why USE CAPTCHAS
Well to completely understand its usage one can consider this
story. Few years ago(November 99) www.Slashdot.org(a
popular site in US) conducted following poll on internet.
Now students at CMU and MIT instantly wrote a program
which increased their vote counts using software and
ultimately the poll had to be taken down because both
MIT and CMU had millions of votes while others
struggled to reach thousands.
There are situations like these where you need to
distinguish whether user is a machine or a computer.
This is where we use CAPTCHAS.
UE6858 Page 7

8. UE6858
“CAPTCHAS”
DEFINITIONS
CAPTCHA stands for
Completely Automated Public Turing test to tell Computers
and Humans Apart
A.K.A. Reverse Turing Test, Human Interaction Proof
Turing Test: to conduct this test two people and a machine is
needed here one person acts as an interrogator sitting in a
separate room asking questions and receiving responses and
goal of machine is to fool the interrogator.
The challenge here: develop a software program that can
create and grade challenges most humans can pass but
computers cannot.
UE6858 Page 8

9. UE6858
“CAPTCHAS”
Types of CAPTCHAS
There are basically 3 types of CAPTCHAS
1.Text Based: These are the most commonly used
CAPTCHAS. It can be further be divided into 3 parts:
GIMPY : Initially used by yahoo ,in this CAPTCHA two steps
are followed as:
a) Pick a word or words from a small dictionary
b) Distort them and add noise and background
GIMPY-R: This was used by google and was basically a simple
advance over gimpy. Here instead of a complete word
individual letters are noised instead of complete words. steps
followed are as
a) Pick random letters
b) Distort them, add noise and background
SIMARD’S: here further advances made and arcs being made
into it ie. Curved geometrical shapes. Hence steps followed are
as
a)Pick random letters and numbers
b)Distort them and add arcs
UE6858 Page 9

10. UE6858
“CAPTCHAS”
2. Graphic Based CAPTCHAS :These are based on graphics
ie. Images symbols and again is of two types:
Bongo
Following steps are followed in BONGO CAPTCHAS as:
a)Display two series of blocks
b)User must find the characteristic that sets the two series
apart
c)User is asked to determine which series each of four single
blocks belongs to.
PIX
This is the second kind of graphics CAPTCHA using distorted
images. Steps followed in its usage are as
a) Create a large database of labeled images
b) Pick a concrete object
c) Pick four images of the object from the images database
d) Distort the images
e) Ask the user to pick the object for a list of words
3.Audio Based CAPTCHAS:
These are based on humans ability to depict sounds that may
be distorted, following algorithm is followed in using it:
a) Pick a word or a sequence of numbers at random
b) Render them into an audio clip using a TTS software
UE6858 Page 10

11. UE6858
“CAPTCHAS”
c) Distort the audio clip
d) Ask the user to identify and type the word or numbers
MAJOR AREAS OF APPLICATIONS:
CAPTCHAs have several applications for practical security,
including (but not limited to):
• Preventing Comment Spam in Blogs. Most bloggers
are familiar with programs that submit bogus comments,
usually for the purpose of raising search engine ranks of
some website (e.g., "buy penny stocks here"). This is called
comment spam. By using a CAPTCHA, only humans can
enter comments on a blog. There is no need to make users
sign up before they enter a comment, and no legitimate
comments are ever lost!
• Protecting Website Registration. Several companies
(Yahoo!, Microsoft, etc.) offer free email services. Up until a
few years ago, most of these services suffered from a
specific type of attack: "bots" that would sign up for
thousands of email accounts every minute. The solution to
this problem was to use CAPTCHAs to ensure that only
humans obtain free accounts. In general, free services
should be protected with a CAPTCHA in order to prevent
abuse by automated scripts.
• Protecting Email Addresses From Scrapers.
Spammers crawl the Web in search of email addresses
posted in clear text. CAPTCHAs provide an effective
mechanism to hide your email address from Web scrapers.
The idea is to require users to solve a CAPTCHA before
showing your email address. A free and secure
UE6858 Page 11

12. UE6858
“CAPTCHAS”
implementation that uses CAPTCHAs to obfuscate an email
address can be found at reCAPTCHA MailHide.
• Online Polls. In November 1999, http://www.slashdot.org
released an online poll asking which was the best graduate
school in computer science (a dangerous question to ask
over the web!). As is the case with most online polls, IP
addresses of voters were recorded in order to prevent single
users from voting more than once. However, students at
Carnegie Mellon found a way to stuff the ballots using
programs that voted for CMU thousands of times. CMU's
score started growing rapidly. The next day, students at MIT
wrote their own program and the poll became a contest
between voting "bots." MIT finished with 21,156 votes,
Carnegie Mellon with 21,032 and every other school with
less than 1,000. Can the result of any online poll be trusted?
Not unless the poll ensures that only humans can vote.
• Preventing Dictionary Attacks. CAPTCHAs can also be
used to prevent dictionary attacks in password systems. The
idea is simple: prevent a computer from being able to iterate
through the entire space of passwords by requiring it to solve
a CAPTCHA after a certain number of unsuccessful logins.
This is better than the classic approach of locking an
account after a sequence of unsuccessful logins, since doing
so allows an attacker to lock accounts at will.
• Search Engine Bots. It is sometimes desirable to keep
webpages unindexed to prevent others from finding them
easily. There is an html tag to prevent search engine bots
from reading web pages. The tag, however, doesn't
guarantee that bots won't read a web page; it only serves to
UE6858 Page 12

13. UE6858
“CAPTCHAS”
say "no bots, please." Search engine bots, since they usually
belong to large companies, respect web pages that don't
want to allow them in. However, in order to truly guarantee
that bots won't enter a web site, CAPTCHAs are needed.
• Worms and Spam. CAPTCHAs also offer a plausible
solution against email worms and spam: "I will only accept
an email if I know there is a human behind the other
computer." A few companies are already marketing this idea
ReCAPTCHA
UE6858 Page 13

14. UE6858
“CAPTCHAS”
ReCAPTCHA is a free CAPTCHA service that helps to digitize
books, newspapers and old time radio shows
About 200 million CAPTCHAs are solved by humans around the
world every day. In each case, roughly ten seconds of human
time are being spent. Individually, that's not a lot of time, but in
aggregate these little puzzles consume more than 150,000 hours
of work each day. What if we could make positive use of this
human effort? ReCAPTCHA does exactly that by channeling the
effort spent solving CAPTCHAs online into "reading" books.
To archive human knowledge and to make information more
accessible to the world, multiple projects are currently digitizing
physical books that were written before the computer age. The
book pages are being photographically scanned, and then
transformed into text using "Optical Character Recognition"
(OCR). The transformation into text is useful because scanning a
book produces images, which are difficult to store on small
devices, expensive to download, and cannot be searched. The
problem is that OCR is not perfect.
ReCAPTCHA improves the process of digitizing books by sending
words that cannot be read by computers to the Web in the form of
CAPTCHAs for humans to decipher. More specifically, each word
that cannot be read correctly by OCR is placed on an image and
used as a CAPTCHA. This is possible because most OCR
programs alert you when a word cannot be read correctly.
But if a computer can't read such a CAPTCHA, how does the
system know the correct answer to the puzzle? Here's how: Each
new word that cannot be read correctly by OCR is given to a user
in conjunction with another word for which the answer is already
known. The user is then asked to read both words. If they solve
the one for which the answer is known, the system assumes their
answer is correct for the new one. The system then gives the new
image to a number of other people to determine, with higher
confidence, whether the original answer was correct
UE6858 Page 14

15. UE6858
“CAPTCHAS”
BREAKING OF CAPTCHAS
UE6858 Page 15

16. UE6858
“CAPTCHAS”
There are two methods used till now to break these CAPTCHAS one
uses decoding software’s which removes noise and other uses humans
1. Some text based CAPTCHAs have been broken by software which
has 3 properties as :
PreProcessing : Removal of background clutter and noise
Segmentation : Splitting the image into regions which each contain
a single character.
Classification: Identifying the character in each region
2. Other CAPTCHAs can be broken by streaming the tests for
unsuspecting users to solve.
UE6858 Page 16

17. UE6858
“CAPTCHAS”
New Proposed Approaches
This new approach is Very similar to PIX CAPTCHAS as discussed
earlier following are the steps followed in using it:
• Pick a concrete object
• Get 6 images at random from images.google.com that match the
object
• Distort the images
• Build a list of 100 words: 90 from a full dictionary, 10 from the
objects dictionary
• Prompt the user to pick the object from the list of words
• Make an HTTP call to images.google.com and search for the
object
• Screen scrape the result of 2-3 pages to get the list of images
• Pick 6 images at random
• Randomly distort both the images and their URLs before
displaying them
• Expire the CAPTCHA in 30-45 seconds
UE6858 Page 17

18. UE6858
“CAPTCHAS”
Benefits of this approach
• The database already exists and is public
• The database is constantly being updated and maintained
• Adding “concrete objects” to the dictionary is virtually
instantaneous
• Distortion prevents caching hacks
• Quick expiration limits streaming hacks
Drawbacks of this approach:
• Not accessible to people with disabilities (which is the case of
most CAPTCHAs)
• Relies on Google’s infrastructure
• Unlike CAPTCHAs using random letters and numbers, the number
of challenge words is limited.
UE6858 Page 18

19. UE6858
“CAPTCHAS”
Conclusion
1.CAPTCHAS are any software that distinguishes human and
machine.
2.Research in CAPTCHAS implies advancement in AI making
computers understand how human thinks.
3.Internet companies are making billions of dollars every year,
their security and services quality matters and so does the
advancement in CAPTCHA technology.
4.Different methods of CAPTCHAS are being studied but new
ideas like ReCAPTCHA using human time on internet is
amazing.
UE6858 Page 19

20. UE6858
“CAPTCHAS”
Bibliography
[i] www.phpcaptcha.org
[ii] www.captcha.net
[iii] www.wikipedia.com
[iv]Research papers by Louis Ahn (Carmegie mellon
university).
UE6858 Page 20