security_image.php

<?php
session_start();

function generate_code(){

    $length = '6';
    $chars = array('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'j', 'k', 'm', 'n', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '2', '3', '4', '5', '6', '7', '8', '9', ',', '@', '$');

    $code = '';
    for ($i=0; $i < $length; $i++){

        $code .= $chars[rand(0, count($chars)-1)];
    }

    $_SESSION['captcha'] = $code;

    return $code;
}

function security_image(){

    $code = isset($_SESSION['captcha']) ? $_SESSION['captcha'] : generate_code();

    $font = 'content/fonts/comic.ttf';

    $width = '110';
    $height = '20';
    $font_size = $height * 0.75;
    $image = @imagecreate($width, $height) or die('GD not installed');

    $background_color = imagecolorallocate($image, 0, 0, 0);
    $text_color = imagecolorallocate($image, 233, 14, 91);


    $textbox = imagettfbbox($font_size, 0, $font, $code);
    $x = ($width - $textbox[4]) / 2;
    $y = ($height - $textbox[5]) / 2;
    imagettftext($image, $font_size, 0, $x, $y, $text_color, $font , $code);


    header('Content-Type: image/png');
    imagepng($image);
    imagedestroy($image);

}

security_image();
?>