Image-captcha - Spam protection with graphic captcha

last update 28.Mar.2010

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Captcha (Graphic)

Spam protection with graphic captcha

Spam protection with Graphic-Captchas

Most of all webmasters, which have contact forms, registration forms or online polls on their websites, know the problem: in a short time they are receiving spam. The reason is, that spammers are using so-called harvesters (also known as webcrawler, spider, robot, or bot). This is a special software, which is searching automatically through the WWW, analyzes websites and tries to fill out any discovered forms with spam.

With Captchas (Completely Automated Public Turing test to tell Computers and Humans Apart), a method, which is able to distinguish between a computer (bot) and a human, it is possible to prevent these spam in most cases.

Conditions of use:
The following scripts are free for use only on private websites. Webmasters of commercial websites are requested to sponsor any amount via Paypal before using these scripts.

A Graphic-Captcha should have at least the following properties:

different font-sizes per character
different fonts per character
rotated, compressed or deformed characters
multicolored background

Requirements:
PHP >= 4.0.6, GD- and FreeType-library, TTF-fonts
The downloadable files do not contain any TTF-font! You can find them on Windows inside the system path: \Windows\Fonts.

Example #1

Info: the use of example 1 is not advisable! Spambots, which are using OCR (optical character recognition), won't have much problems to recognize these 3 characters, because they have the same font-size, and only one background color. Maybe it would be better to use only one font color, because the 3 characters would blend into each other.

Download: example1.zip

Example #2

Info: random font colors and background lines.

Download: example2.zip

Example #3

Info: a sinusoidal function to bend the characters, with image scanning lines displacement.

Download: example3.zip

Example #4

Info: a black scratched line.

Download: example4.zip

Example #5

Info: background characters.

Download: example5.zip

Example #6

Info: a background with color blending.

Download: example6.zip

Example #7

Info: different fonts and font-sizes.

Download: example7.zip

Example #8

Info: background characters.

Download: example8.zip

Example #9

Info: another background.

Download: example9.zip

Example #10

Info: instead of characters, the script asks for the name (in german and english!) of a figure. It's important to choose figures, which have not two or more possible interpretations. E.g. this script shows a picture of an automobile, but what is the right answer: auto, automobile, car, motorcar ?

What is the figure's name?

Download: example10.zip

Example #11