It describe what is CAPTCHA? and how it can be generated and its type.

1. BMS Institute of Technology
&
Management
Presentation
On
CAPTCHA
Presented by:
Sachin Jain
MCA 1st sem
Guided by:
Mr. Ganesh
Asst prof. Department of MCA
BMSIT&M

2. AGENDA
• Introduction
• Origin
• How to generate CAPTCHA
• Types
• Applications
• Advantages
• Disadvantages
• Conclusion
• References

3. INTRODUCTION
 CAPTCHA-Completely Automated Public Turing
test to tell Computer and Human Apart
 A CAPTCHA is a type of challenge response test
used in computing to ensure that response is not
generated by a computer.
 A common type of CAPTCHA requires that the user
type letters or digits from the distorted image that
appears on the screen.

4. ExamplesExamples

5. ORIGIN
 The most common type of CAPTCHA was first
invented in 1997 by Mark D. Lillibridge, Martin
Abadi , Krishna Bharat, and Andrei Z. Broder.
 This form of CAPTCHA requires that the user type
the letters of a distorted image, sometimes with the
addition of an obscured sequence of letters or digits
that appears on the screen.
 The term was coined in 2003 by Luis von
Ahn, Manuel Blum, Nicholas J. Hopper, and John
Langford.

6. HOW TO GENERATE
Picks a random
string of letters:
o m a g
Renders it to a
distorted image:-

7. TYPE THE CHARACTERS
THAT APPEAR IN THE
IMAGE
..... and generates a test

8. o Text Based CAPTCHAs
 Gimpy
 Ez-gimpy
 Baffle text
 Simard’s HIP (MSN)
o Graphics Based CAPTCHAs
 Bongo
 Pix
o Audio or Sound Based CAPTCHAs
TYPES OF CAPTCHA

9. Gimpy:
 Originally designed by Yahoo and CMU.
 Based on human ability to read heavily
distorted and corrupted text.
 Picks up 10 random words from dictionary
and distorts.
 User has to recognize at least 3 words.
 If user is correct, he is admitted.
Fig:-Gimpy CAPTCHA[1]

10. Ez-Gimpy:
A modified version of Gimpy.
Used in Yahoo Messenger Service.
It contains only one random character string.
The word is random and not picked from the
dictionary.
Fig:- Ez-Gimpy CAPTCHA[2]

11. Its provided for Microsoft MSN services.
Uses 8 characters.
Wraping is used to distort.
It is very strongly implemented and hasn’t been
broken.
MSN CAPTCHA
Fig:- MSN CAPTCHA[3]

12. 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.
To which side does the block
on the bottom belong?
BONGO
Fig:- Bongo CAPTCHA[4]

13. Uses a large database of labeled images
It shows a set of images, user has to recognize the
common feature among those.
Ex:- Pick the common characteristic among the
following four pictures
PIX
Fig:- pix CAPTCHA[5]

14. Applications
 Protecting Web Registration
 Preventing comment spam
 Search engine bots
 Preventing Dictionary Attacks

15. • Distinguishes between a human and a machine
• Makes online polls more genuine.
• Reduces spam and viruses
• Makes online shopping safer.
• Diminishes abuse of free email account services.
• Sometimes very difficult to read.
• Are not compatible with users with disabilities.
• Time-consuming to decipher.
• Technical difficulties with certain internet
browsers.
Advantages
Disadvantages

16. CAPTCHAs are an effective way to counter bots and
reduce spam.Some issues with current implementations
represent challenges for future improvements.
Conclusion

17. References
[1] http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha
[2] http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha
[3] http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha
[4] http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha
[5] http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha
[6] https://en.wikipedia.org/wiki/CAPTCHA
[7] http://www.nytimes.com/2002/12/10/science/human-or-computer-take-this-test.html
[8] http://www.captcha.net/captcha_cacm