CAPTCHAIMAGINATION:

A Robust Image Based CAPTCHA Generation

System

Contents:-Introduction

Full Form Definition Example

ApplicationsTypes of

CAPTCHAAdvantagesDisadvantagesConclusion

Introduction

Full Form

C :- Completely

A :- Automated

P :- Public

T :- Turing Test To Tell

C :- Computers And

H :- Humans

A :- Apart

DefinitionA CAPTCHA is a type of challenge-response

test used in computing to ensure that the response is not generated by a computer.

The process usually involves one computer asking a user to complete a simple test which the computer is able to generate and grade.

A common type of CAPTCHA requires that the user type letters or digits from a distorted image that appears on the screen.

Examples

Applications

Preventing comment spam in blogs.

Protecting Website Registration.

Online Polls.

Search Engine Bots.

Filters Worms and Spam.

Types Of CAPTCHA

There are three types of CAPTCHA’s:-

Text Based CAPTCHA.

Graphic Based CAPTCHA.

Audio Based CAPTCHA.

Ez-Gimpy:-A modified version of Gimpy. Used in Yahoo Messenger Service.It contains only one random character string.The word is random and not picked from the

dictionary.

MSN Passport Service CAPTCHAs:-

Its provided for Microsoft MSN services.

Uses 8 characters.

Wraping is used to distort.

Its very strongly implemented and hasn’t

been broken.

Text Based CAPTCHA

Graphic Based CAPTCHABongo

Display two series of blocksUser must find the characteristic that sets the

two series apartUser is asked to determine which series each

of four single blocks belongs to -

Graphic Based CAPTCHA

Dog Pool

Audio Based CAPTCHA

Consist of downloadable audio clip.

User listens and enters the spoken word.

Helps visually disabled users.

Google’s provides an audio enabled

CAPTCHA.

Advantages

CAPTCHA is working as an important internet rectifier system to distinguish genuine users and automated programs.

It avoids accessing of E-mails by thousands of spammers every day.

Fits to theme of the page. Can be written in any language–Perl, .NET, ASP,

JavaScript.

DisadvantagesA person having sight problem will not be

able to respond to CAPTCHA problems efficiently.

Some CAPTCHA images are very difficult to interpret for humans also.

CAPTCHA may not safe against spammers; even spammers can also develop such programs which will be able to understand the patterns of puzzles written by a particular system of CAPTCHA.

ConclusionCAPTCHAs are an effective way to counter

bots and reduce spam. Applications are varied– from stopping bots to

character recognition & pattern matching. Some issues with current implementations

represent challenges for future improvements.

By:-Vinit SharmaB.Tech (2nd Year, C.S )