2.  Introduction to CAPTCHA
 Good CAPTCHA properties
 CAPTCHA uses
 Types of CAPTCHA
 Advantages of existing CAPTCHA
 Disadvantages of existing CAPTCHA
 Geo-CAPTCHA
 Geo-CAPTCHA Passing HIP test Condition

3.  CAPTCHA -Completely Automated Public
Turing test to tell Computers and
Humans Apart.
 CAPTCHA program generates the challenges.
 It recognize the humans’ behaviours.
 It tells humans and computers apart.

4.  Security:The security dimension determines
its strength for preventing the variant attacks.
 Usability: usability dimension determines the
necessity of ”user friendly” when CAPTCHA is
deployed

5. CATCHA has been used extensively in online
applications:
 Online Ticket Reservation,
 Online Polls,
 Online Banking,
 Web-based E-mail Service

6.  Text based CAPTCHA
 Image based CAPTCHA

7.  It makes impossible for computers to pass
the CAPTCHA challenges.
 It prevent Botnet attacks.
 It prevents the spam attacks.

8. Existing CAPTCHA is vulnerable to :
 The third Party Human Attack
 Binarization
 Vertical Segmentation
 Phishing, Session Hijacking, Relay Attacks
and Man in the Middle Attacks
 Key-logger and Hidden Camera

9.  Its personalized image base CAPTCHA.
 It identifies Legitimate and Illegitimate users.
 It generates lot of personalized challenges which
makes it suitable for cloud computing applications.
 It non-recordable & OCR can’t defeat it.
 Its specifically designed to deal with third party
attacks.
 It also prevents Automatic programming attacks.

10.  Idea :To use a geographic scene image.
 Image is privately known to each user.
 Working : Generates a set of candidate
images for a location selected by each user.
 User selects a geo-location image from the
set .
 This is registered private image to be used as
the correct answer to the challenges.

11.  The challenges are vertically and horizontally
rotated images of the registered private
image.
Fig(1)The random challenge
of any angle
Fig(2)The rotated solution
of correct angle street
view

12.  Condition :Security threshold condition
if | GH(x)- GH(y) <= T | then pass HIP test.
 GH(x)- denotes the function to calculate the hash
value of image x.
 GH(y)- denotes the function to calculate the hash
value of image y.
 T- we define a error threshold .

13. 1. U User’s log-in account;
2. PW User’s log-in password;
3. A Pick a personalized Geo-location
image which only known to the user;
4. Qu
x and Qu
y C(A);
5. R G(Qu
x;Qu
y);
6. S Pick a solution image from R;
7. Save the h, p , (Qu
x; Qu
y ), U and PW to
database;

14.  U User’s log-in account;
 while U is true do
 Qu
x and Qu
y M(U);
 end while
 R G(Qu
x; Qu
y );
 C Randomize(R);

15. Challenge
Quantity
Challenge can
be recorded
Broken by OCR
Typical
CAPTCHA
Plenty &
Dynamic
No Text-based: Yes
Image-based:
No
Personalized
challenge
Fixed & Static Yes Yes
Geo-CAPTCHA Fixed & Dynamic No No

16. Automatic
Attack
Genuine User
(Human)
3rd Party
Human
Typical
CAPTCHA
Fail Pass Pass
Personalized
Challenge
Pass Pass Fail
Geo-CAPTCHA Fail Pass Fail