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CAPTCHA

Something That Human Can Do But
Computers Can’t………..

Presented By : Shreya
2
Definition
CAPTCHA stands for Completely Automated


Public Turing test to tell Computers and Humans
Apart
A program tha...
Background
 First used by Altavista in1997
Reduced SPAM add-url by over 95%
 CMU/Yahoo!
Automated the creating and gra...
Background
CAPTCHAs are based on open AI problems
Breaking CAPTCHAs help advance AI by

solving these open problems
Imp...
Applications
Free email services
Online polls
Dictionary attacks
Newsgroups, Blogs, etc…
SPAM

6
Types of CAPTCHAs
Text based
Gimpy, ez-gimpy
Gimpy-r, Google CAPTCHA
Simard’s HIP (MSN)

Graphic based
Bongo
Pix

...
Text Based CAPTCHAs
Gimpy, ez-gimpy
Pick a word or words from a small dictionary
Distort them and add noise and backgro...
Text Based CAPTCHAs

9
Graphic Based CAPTCHAs
Bongo
Display two series of blocks
User must find the characteristic that sets the two

series a...
Graphic Based CAPTCHAs
PIX
Create a large database of labeled images
Pick a concrete object
Pick four images of the ob...
Graphic Based CAPTCHAs

Dog

Pool

12
Audio Based CAPTCHAs
Pick a word or a sequence of numbers at random
Render them into an audio clip using a TTS software
...
Breaking CAPTCHAs
Most text based CAPTCHAs have been broken by

software
OCR

Segmentation

Other CAPTCHAs were broken...
Properties


CAPTCHA should be automatically generated
and graded
 Test can be taken quickly and easily by human
users
...
Final Thoughts
They are crucial to preventing boot attacks
Hopefully, they will become more user-friendly to

people wit...
Bibliography……

17
18
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Transcript of "Shreya"

  1. 1. CAPTCHA Something That Human Can Do But Computers Can’t……….. Presented By : Shreya
  2. 2. 2
  3. 3. Definition CAPTCHA stands for Completely Automated  Public Turing test to tell Computers and Humans Apart A program that can tell whether its user is a human or a computer. The challenge: develop a software program that can create and grade challenges most humans can pass but computers cannot 3
  4. 4. Background  First used by Altavista in1997 Reduced SPAM add-url by over 95%  CMU/Yahoo! Automated the creating and grading of challenges  PARC Relies on document image degradation to prevent successful OCR Conducted user-focused studies to assess the effectiveness of CAPTCHAs 4
  5. 5. Background CAPTCHAs are based on open AI problems Breaking CAPTCHAs help advance AI by solving these open problems Improving CAPTCHAs help telling computers and human apart Win-win situation 5
  6. 6. Applications Free email services Online polls Dictionary attacks Newsgroups, Blogs, etc… SPAM 6
  7. 7. Types of CAPTCHAs Text based Gimpy, ez-gimpy Gimpy-r, Google CAPTCHA Simard’s HIP (MSN) Graphic based Bongo Pix Audio based 7
  8. 8. Text Based CAPTCHAs Gimpy, ez-gimpy Pick a word or words from a small dictionary Distort them and add noise and background Gimpy-r, Google’s CAPTCHA Pick random letters Distort them, add noise and background Simard’s HIP Pick random letters and numbers Distort them and add arcs 8
  9. 9. Text Based CAPTCHAs 9
  10. 10. Graphic Based CAPTCHAs Bongo Display two series of blocks User must find the characteristic that sets the two series apart User is asked to determine which series each of four single blocks belongs to Difference? thick vs. thin lines 10
  11. 11. Graphic Based CAPTCHAs PIX Create a large database of labeled images Pick a concrete object Pick four images of the object from the images database Distort the images Ask the user to pick the object for a list of words 11
  12. 12. Graphic Based CAPTCHAs Dog Pool 12
  13. 13. Audio Based CAPTCHAs Pick a word or a sequence of numbers at random Render them into an audio clip using a TTS software Distort the audio clip Ask the user to identify and type the word or numbers 13
  14. 14. Breaking CAPTCHAs Most text based CAPTCHAs have been broken by software OCR Segmentation Other CAPTCHAs were broken by streaming the tests for unsuspecting users to solve. 14
  15. 15. Properties  CAPTCHA should be automatically generated and graded  Test can be taken quickly and easily by human users  Test will accept virtually all human users and reject software agents  Test will resist automatic attack for many years despite the technology advances and prior knowledge of algorithms
  16. 16. Final Thoughts They are crucial to preventing boot attacks Hopefully, they will become more user-friendly to people with disabilities (visual, mental) CAPTCHA’s are mainly produced from AJAX and PHP technology Various algorithms are present Use of XML
  17. 17. Bibliography…… 17
  18. 18. 18
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