“Creating this website I attracted lots of spambots to flood my forum, my programming resources, freelance database and other forms, but you probably know this situation very well. So I decided to create a simple PHP Class which could help me and probably other people to deal with the spam.” 
I. DESCRIPTION
Image Validator is a GPL CAPTCHA php script to stop spam on any form: comment areas, sign-ups, shopping carts - any area of your website where you fear the evil spammers may target.
II. REQUIREMENTS
1. Apache 1 or 2
2. PHP 4 or 5
3. GD 2 with truetype support
III. INSTALLATION
0. Unpack this package.
1. You may edit _config.php file located in imgval directory.
2. You may copy some TrueType fonts in imgval/fonts directory.
2. Upload or copy imgval directory to browsable directory.
3. Open imgval/index.php in your browser for testing.
IV. INTEGRATION NOTES
In <img> tag, ’src’ parametter should be linked with imgval/code.php.
Example: <img src=”imgval/code.php” />.
To prevent cache images you may add some unique parameter.
Example: <img src=”imgval/code.php?id=<?= time() ?>” />
Your should start a session in the response PHP file. In the valid action
PHP source code you should verify MD5 sum of the input-code-field-value
with session variable named __img_code__
Example:
if (md5($_POST['code']) == $_SESSION['__img_code__'])
echo “Valid code”;
else
echo “Invalid code”;