introduction about captcha and its types
DESCRIPTION
this presentation contains basic information about captcha, its types, where it is used and how to break captchaTRANSCRIPT
![Page 1: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/1.jpg)
CAPTCHA
-By Bansari Rajani
![Page 2: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/2.jpg)
Contents...•What is CAPTCHA?•Making a CAPTCHA•Type of CAPTCHA•Where to use CAPTCHA?•Guidelines when making a CAPTCHA•Ways to break CAPTCHA•reCAPTCHA•Time spent
![Page 3: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/3.jpg)
CAPTCHA means...
Completely Automated Public Turing test to tell Computers and Humans Apart
Created in 2000 for Yahoo to prevent automated e-mail account registration.
![Page 4: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/4.jpg)
Cont...A program that can tell whether its user is a human or a computer.
It uses a type of challenge-response test to determine that the response is not generated by a computer.
![Page 5: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/5.jpg)
Turing test:“Standard Interpretation”
Player C, the interrogator is asked with trying to determine which player A or B is a computer and which is a human.
![Page 6: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/6.jpg)
Reverse Turing Test:A CAPTCHA is sometimes described as a Reverse Turing Test, because it is...
Administrate by a machine and targeted to a human
![Page 7: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/7.jpg)
So, CAPTCHA is...
A program that can generate and grade tests that:
•Most human can pass;•Current computer programs cannot pass
![Page 8: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/8.jpg)
Making a CAPTCHA...
Pick a random string of characters
Renders it into a distorted image
CAPTCHA
![Page 9: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/9.jpg)
Making a CAPTCHA...
...and the program generates a test:
Type the characters that appear in the image
![Page 10: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/10.jpg)
Type of CAPTCHA...
•Early CAPTCHAs
•Generated by EZ-gimpy program;•Used previously in Yahoo!
![Page 11: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/11.jpg)
Type of CAPTCHA...•Improved CAPTCHAs:
• high contrast for human readability;
• medium, per-character perturbation;
• random fonts per character;
![Page 12: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/12.jpg)
Type of CAPTCHA...•A Morden CAPTCHAs:
•rather than attempting to create a distorted background and high levels of warping on the text;•focus on making segmentation difficult by adding an angled line;
![Page 13: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/13.jpg)
Other types of CAPTCHA...
•Animated CAPTCHAs
•3D CAPTCHAs
•ASCII Art
![Page 14: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/14.jpg)
Where to use CAPTCHAs???
•Data connection•Worms and spam•Protecting Email address from scrappers•Online polls•Protecting website registration•Preventing dictionary attacks•Search engine bots
![Page 15: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/15.jpg)
Guidelines when making a CAPTCHA...
•Image security : Image of text distorted randomly•Script level security : Systems where a solution to the same CAPTCHA can be
used multiple times
![Page 16: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/16.jpg)
Guidelines when making a CAPTCHA...Accessibility : It prevent visually impaired users from accessing the protected resource
•They use screen reader, so when you reached an image, all it can do is to read the caption of that image•Solution: permitting users to opt for an audio or sound CAPTCHA
![Page 17: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/17.jpg)
Ways to break CAPTCHAs...•Using cheap human labor to process the tests•Improving Character Recognition software (OCR – Optical Character Recognition )
![Page 18: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/18.jpg)
Break: character recognition...•Programs that have the following functions:• Extraction of the image from the web page • Removal of background clutter, for example with color filters and detection of thin lines • Segmentation, i.e. splitting the image into regions each containing a single letter;• Identifying the letter for each region.
![Page 19: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/19.jpg)
reCAPTCHA...•New form of CAPTCHA that also helps digitize books;•The words displayed to the user come directly from old books that are being digitized; •Words that OCR could not identify;
![Page 20: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/20.jpg)
![Page 21: Introduction about Captcha and its types](https://reader035.vdocuments.net/reader035/viewer/2022081519/55903ec41a28aba96a8b46a6/html5/thumbnails/21.jpg)
Time spent...•Roughly 60 million CAPTCHAs are solved each day;
•Medium 10 seconds to solve a captcha;
•People around the world waste more than 150,000 hours on solving CAPTCHAs;