captcha presentation

1. Presented by:-
BHAVANA SHARMA
B.Tech final year, CSE

2. Full Form Of CAPTCHA
C - Completely
A - Automated
P - Public
T - Turing Test To Tell
C - Computers And
H - Humans
A - Apart

3. Definition Of CAPTCHA
 A CAPTCHA is a challenge response test that
determines whether a user is human or an automated
program.
 A CAPTCHA differentiates between human and
automated program by setting some task that is easy
for most humans to perform but is more difficult and
time consuming for current automated programs to
complete.

4. History Of CAPTCHA
In 1997, the AltaVista team comprised of Lillibridge,
Adabdi, Bharat and Broder, began work on a system to
prevent Internet bots.
The second team, comprised of Luis von Ahn, Manuel
Blum, Nicholas J. Hopper and John Langford gave birth to
the term CAPTCHA in 2003.

5. Characteristics Of CAPTCHA
 It should be easy for human users to pass.
 It should be easy for a tester machine to generate and
grade.
 It should be hard for a software robot to pass.

6. Types Of CAPTCHA
Types Of
CAPTCHA
Text
CAPTCHA
Puzzle
CAPTCHA
Image
CAPTCHA
Audio
CAPTCHA
Video
CAPTCHA

7. Text CAPTCHA
It can consist of simple questions that are easy
to answer, or show a distorted image of a word,
also easy for humans to discern but difficult for
bots.

8. Example Of Text CAPTCHA

9. Example Of Text CAPTCHA
63

10. Advantages Of Text CAPTCHA
 Text based CAPTCHAs is very simple to implement.
 It is very effective.
For example:-
 What is three plus two(3+2=?)
 Which of cabbage, apple and table is vegetable?

11. Disadvantages Of Text CAPTCHA
 In text images, user has some problems to identify
the correct text or characters.
 Multiple fonts
 Font size
 Blurred letters

12. Image CAPTCHA
Image based CAPTCHAs are challenge tests in
which the users have to guess images.
In image based CAPTCHAs user identify the image.

13. Example Of Image CAPTCHA

14. Example Of Image CAPTCHA

15. Advantages Of Image CAPTCHA
The advantage of image based CAPTCHA is that
pattern recognition is hard AI problem and therefore it
is difficult to break this test using pattern recognition
technique.

16. Disadvantages Of Image CAPTCHA
Some users face problem of image identification
who have low vision or due to blurring of images.

17. Audio CAPTCHA
 Require user to solve a speech recognition test.
 In this version of CAPTCHA letters are read aloud
instead of being displayed in image.

18. Example Of Audio CAPTCHA
a x 8 l g

19. Advantages Of Audio CAPTCHA
Audio CAPTCHAs were very useful for visually
disabled users.

20. Disadvantages Of Audio CAPTCHA
It is available in English therefore end user must
have a comprehensive English vocabulary.
Character that have similar sound.

21. Video CAPTCHA
Video based CAPTCHA’s will show a video, and then
ask for three words which best describe the video.
This , of course , can have major drawbacks as it expects
the correct answer on something where opinions can
greatly vary.

23. Advantages Of Video CAPTCHA
Video CAPTCHAs are used in commercial and
academic applications.

24. Disadvantages Of Video CAPTCHA
Due to large size of file, users face problem to
download video and find correct CAPTCHA.

25. Puzzle CAPTCHA
Puzzle CAPTCHA is unique in that it is an image
split up into different pieces like a puzzle, and it
uses java script to allow the user to drag and drop
the pieces of the puzzle to put them in the correct
order.

26. Example of puzzle CAPTCHA

28. Disadvantages Of Puzzle CAPTCHA
The task is not easy for users because puzzle based
CAPTCHA take more time to solve the puzzle and
identify actual arrangement of puzzles.

29. CAPTCHA logic:-
Generate the question
Persist the correct answer
Present the question to user
Evaluate answer, if incorrect , start again,
generate a different CAPTCHA
If correct allow access to user

30. Applications Of CAPTCHA
Preventing comment spam in blogs.
Protecting website registration.
Protecting email addresses.

31. Advantages Of CAPTCHA
 Distinguishes between a human and a machine.
 Reduces spam and viruses.
 Makes online shopping safer.

32. Disadvantages Of CAPTCHA
 Sometimes very difficult to read.
 Time-consuming to decipher.
 Technical difficulties with certain internet browsers.