security through obscurity

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ABSTRACT: Web sites are increasingly under attack from automated scripts. This topic covers how Web professionals can combat certain automated attacks with CAPTCHA. In many cases, sites could deter automated attacks if they could distinguish human users from machine users.
Artificial Intelligence experts identify a category of security controls called “CAPTCHAs” which can help Web sites distinguish between human and machine users. A common kind of CAPTCHA that is used on websites requires that the visitor type the letters and numbers of a distorted image. This method is based on the fact that is difficult for computers to extract the text from the image while it is very easy for humans.


INTRODUCTION


A CAPTCHA (Completely Automated Public Turing Test to Tell Computers and Humans Apart) is a program that generates and grades tests that are human solvable, but intends to be beyond the capabilities of current computer programs. The term "CAPTCHA" was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford of Carnegie Mellon University. At the time, they developed the first CAPTCHA to be used by Yahoo.
This technology is now almost a standard security mechanism for defending against undesirable Internet bots programs, such as those spreading junk emails and those grabbing thousands of free email accounts instantly. It has found widespread application on numerous commercial web sites including Google, Yahoo , and Microsoft’s MSN.


2.Captcha code creator, PHP captcha script
Captcha Creator is a powerful and complete PHP Captcha Script that generates Captcha Images. Easy to install on any web hosting account, it is very customizable and easy to configure. You can specify the size of the image, the color of text and backgrounds, the fonts used, the number of letters and numbers displayed, backgrounds, and much more.

Why Captcha Creator?
Captcha Creator is an easy to use PHP Script that generates Strong Captchas, which has NOT been broken yet. We update our script often, and we offer a large collection of backgrounds, fonts, and configuration files that have various text sizes and positions, to ensure that is it very difficult, if not impossible, for spam bots to break it.
Is very easy to install on any website with php support, and can be used to stop web forms submissions made by spam bots on sites like: Guestbooks, Blogs, Wiki, Comments, Feedback forms, etc
After uploading the script to your website, you can use it on your existing web form by following three easy steps.


3.TYPES OF CAPTCHA

By far, the most common type of CAPTCHA involves the use of letters that are arranged randomly and are distorted in some way with various background colors. These are the ones that you will most likely have seen when signing up for an e¬mail account. But actually, other alternatives do exist .


3.1Character¬Based CAPTCHA

This category means that a string of characters is presented to the user. This string can contain either words or random alphanumeric characters (See