Published on

1 Comment
1 Like
  • can you please mail me this at
    Are you sure you want to  Yes  No
    Your message goes here
No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide


  1. 1. CAPTCHA Presented By : Ashish Madhok MCA-2 SEM 13097019
  2. 2. Topics To be Covered : 1). What is a CAPTCHA ? 2). Why it is useful? 3). About CAPTCHA 4). Origin 5). Applications 6). Characteristics 7). Accessibility
  3. 3. 8). Circumvention 9). Help against spam 10). Need of a CAPTCHA 11). CAPTCHA-Pros and Cons 12). Guidelines
  4. 4. WHAT IS A CAPTCHA ? <ul><li>C ompletely A utomated P ublic T uring test to tell C omputers and H umans A part </li></ul><ul><li>An automated test that can distinguish between machines and humans online. </li></ul><ul><li>A type of challenge-response test. </li></ul><ul><li>Involves one computer (a server). </li></ul>
  5. 5. <ul><li>Simple Verification made up of:- </li></ul><ul><li>The CAPTCHA image and the CAPTCHA code that generates it. </li></ul><ul><li>A form field into which the code one sees in the CAPTCHA image must be inserted – and an enter button. </li></ul><ul><li>A separate code which checks that the code inserted manually into the field was correct. </li></ul>
  6. 6. WHY IS IT USEFUL ? <ul><li>Designed to prevent BOTS from abusing internet services…BOTS </li></ul><ul><li>Defend e-commerce systems from bots. Eg-Yahoo. </li></ul><ul><li>Requirement of a common type of CAPTCHA. </li></ul><ul><li>Described as Reverse Turing Test. </li></ul>
  7. 7. ABOUT CAPTCHA ! <ul><li>Pessimal Print </li></ul><ul><li>Create a distorted background. </li></ul><ul><li>High levels of warping on the text. </li></ul><ul><li>Baffle Text </li></ul><ul><li>Focuses on making segmentation difficult by adding an angled line. </li></ul>
  8. 8. ORIGIN <ul><li>Controlled access to web services in a 1996 manuscript of Moni Naor. </li></ul><ul><li>A simple CAPTCHA-developed in 1995 by Anton Lam. </li></ul><ul><li>Other primitive CAPTCHA-developed in 1997 at Alta Vista by Andrei Broder. </li></ul><ul><li>Developed in 2000 by Vin Ahn and Blum </li></ul>
  9. 9. APPLICATIONS <ul><li>1). Preventing Comment Spam in Blogs. </li></ul><ul><li>2). Protecting Website Registration. </li></ul><ul><li>3). Online Polls. </li></ul><ul><li>4). Preventing Dictionary Attacks. </li></ul><ul><li>5). Search Engine Bots. </li></ul><ul><li>6). Worms and Spam. </li></ul>
  10. 10. CHARACTERISTICS <ul><li>Current computers are unable to accurately solve. </li></ul><ul><li>Most humans can solve. </li></ul><ul><li>Does not rely on attacker never having seen the CAPTCHA before. </li></ul><ul><li>Is able to automatically generate new challenges that require artificial intelligence techniques to solve. </li></ul>
  11. 11. CIRCUMVENTION <ul><li>Few approaches to defeat CAPTCHA :- </li></ul><ul><li>HUMAN SOLVERS </li></ul><ul><li>INSECURE IMPLEMANTATION </li></ul><ul><li>COMPUTER CHARACTER RECOGNITION </li></ul>
  12. 12. HOW CAN CAPTCHA HELP AGAINST SPAM? <ul><li>Great help in downsizing or diminishing FORM SPAMMING </li></ul><ul><li>Bots go around the web </li></ul><ul><li>Find forms </li></ul><ul><li>Send thousands of e-mails through that </li></ul><ul><li>Fill in the form – sign up for 100 free email accounts, services or products. </li></ul>
  13. 13. IMAGE-RECOGNITION CAPTCHAs <ul><li>Alternative for text based CAPTCHAs </li></ul><ul><li>POTENTIAL PROBLEMS :- </li></ul><ul><li>Difficult for a small site to acquire a large dictionary of images. </li></ul><ul><li>Ask the user to make a binary choice. </li></ul>
  14. 14. PROS AND CONS <ul><li>PROS </li></ul><ul><li>Help to fight automatic bots from spamming web site forms. </li></ul><ul><li>CONS </li></ul><ul><li>Not a 100 % spammer proof system </li></ul><ul><li>Not safe for bank account details or credit card pins </li></ul><ul><li>Sometimes humans can’t recognize it. </li></ul>
  15. 15. GUIDELINES <ul><li>Accessibility </li></ul><ul><li>Image Security </li></ul><ul><li>Script Security </li></ul>
  16. 16. THANK YOU !!!