$background = imagecolorallocate($image, 0, 0, 0);
// Make background transparent by setting the colour we are going to use as transparent
imagecolortransparent($image, $background);
// Fill it in with the background colour. This is required to make the background transparent
imagefilledrectangle($image, 0, 0, 199, 49, $background);
// function to generate captcha characters
function captchaChars($hash)
{
// Generate a 32 character string by getting the MD5 hash of the servers name with the hash added to the end.
// Adding the servers name means outside sources cannot just work out the characters from the hash
$captchastr = md5($_SERVER['SERVER_NAME'] . $hash);
return strtoupper($captchastr);
// Make all our characters uppercase for clarity in the image
}
// Lets get the characters to show in the image or say 'error' if no hash submitted
$str = !empty($_GET['hash']) ? captchaChars($_GET['hash']) : 'ERROR';
// Assign a colour for the text and lines. I've chosen a shade of grey
$our_colour = imagecolorallocate($image, 140, 140, 140);
// Lets add three random background lines
for ($i = mt_rand(5, 8); $i <= 29; $i += 10) {
imageline($image, mt_rand(0, 100), $i + mt_rand(-5, 5), mt_rand(0, 100), $i + mt_rand(-5, 5), $our_colour);
}
// Set a random horizontal starting position
$x_pos = mt_rand(10, 20);
// Lets loop through our string adding one character at a time in a randomish position
// We start with the first character and then use every seventh character just for added randomness
for ($i = 0; $i <= 28; $i += 7) {
imagestring($image, 5, $x_pos, mt_rand(0, 12), $str[$i], $our_colour);
// add a character from our string
$x_pos += mt_rand(10, 18);
// Move the horizontal position by a random amount
if (isset($_POST['submit'])) {
$hash = !empty($_POST['hash']) ? preg_replace('/[\\W]/i', '', trim($_POST['hash'])) : '';
// Remove any non alphanumeric characters to prevent exploit attempts
$captchacode = !empty($_POST['captchacode']) ? preg_replace('/[\\W]/i', '', trim($_POST['captchacode'])) : '';
// Remove any non alphanumeric characters to prevent exploit attempts
// function to check the submitted captcha
function captchaChars($hash)
{
// Generate a 32 character string by getting the MD5 hash of the servers name with the hash added to the end.
// Adding the servers name means outside sources cannot just work out the characters from the hash
$captchastr = strtolower(md5($_SERVER['SERVER_NAME'] . $hash));
$captchastr2 = '';
for ($i = 0; $i <= 28; $i += 7) {
$captchastr2 .= $captchastr[$i];
}
return $captchastr2;
}
if (!empty($captchacode)) {
if (strtolower($captchacode) == captchaChars($hash)) {
echo '<h3>The submitted characters were correct</h3>';
} else {
echo '<h3>The submitted characters were WRONG!</h3>';
}
} else {
echo '<h3>You forgot to fill in the code!</h3>';
}
}
?>
</div>
</body>
</html>
