PHP Captcha Security Images

[tuidangvui]

<?php
class CaptchaSecurityImages {

var $font = 'monofont.ttf';

function generateCode($characters) {
/* list all possible characters, similar looking characters and vowels have been removed */
$possible = '23456789bcdfghjkmnpqrstvwxyz';
$code = '';
$i = 0;
while ($i < $characters) {
$code .= substr($possible, mt_rand(0, strlen($possible)-1), 1);
$i++;
}
return $code;
}

function CaptchaSecurityImages($width='120',$height='40',$c haracters='6') {
$code = $this->generateCode($characters);
/* font size will be 75% of the image height */
$font_size = $height * 0.75;
$image = @imagecreate($width, $height) or die('Cannot initialize new GD image stream');
/* set the colours */
$background_color = imagecolorallocate($image, 255, 255, 255);
$text_color = imagecolorallocate($image, 20, 40, 100);
$noise_color = imagecolorallocate($image, 100, 120, 180);
/* generate random dots in background */
for( $i=0; $i<($width*$height)/3; $i++ ) {
imagefilledellipse($image, mt_rand(0,$width), mt_rand(0,$height), 1, 1, $noise_color);
}
/* generate random lines in background */
for( $i=0; $i<($width*$height)/150; $i++ ) {
imageline($image, mt_rand(0,$width), mt_rand(0,$height), mt_rand(0,$width), mt_rand(0,$height), $noise_color);
}
/* create textbox and add text */
$textbox = imagettfbbox($font_size, 0, $this->font, $code) or die('Error in imagettfbbox function');
$x = ($width - $textbox[4])/2;
$y = ($height - $textbox[5])/2;
imagettftext($image, $font_size, 0, $x, $y, $text_color, $this->font , $code) or die('Error in imagettftext function');
/* output captcha image to browser */
header('Content-Type: image/jpeg');
imagejpeg($image);
imagedestroy($image);
$_SESSION['security_code'] = $code;
}

}

$width = isset($_GET['width']) ? $_GET['width'] : '120';
$height = isset($_GET['height']) ? $_GET['height'] : '40';
$characters = isset($_GET['characters']) && $_GET['characters'] > 1 ? $_GET['characters'] : '6';

$captcha = new CaptchaSecurityImages($width,$height,$characters);

?>

Sử dụng .htaccess
RewriteEngine onRewriteRule captcha.jpg /CaptchaSecurityImages.phpCaptchaSecurityImages.php

<img src="CaptchaSecurityImages.php" alt="" />Security Code:<input id="security_code" name="security_code" type="text" />

session_start();if(($_SESSION['security_code'] == $_POST['security_code']) && (!empty($_SESSION['security_code'])) ) { unset($_SESSION['security_code']);} else { // Insert your code for showing an error message here}