生成验证码

啥也不说，直接上代码

class Captcha
{

    /**
     * 生成验证码
     *
     * @param int $length 码字符长度
     * @param int $width 宽度
     * @param int $height 长度
     * @param string $type 类型
     * @return string
     */
    public static function createCode($length = 4, $width = 45, $height = 30, $type = 'png')
    {
        session_start();
        $code = self::randCode($length);
        $_SESSION['captcha'] = $code;
        $img = @imagecreatetruecolor($width, $height); //新建一个真彩色图像
        //画一矩形并填充
        $color = imagecolorallocate($img, mt_rand(200, 255), mt_rand(200, 255), mt_rand(200, 255));
        @imagefilledrectangle($img, 0, 0, $width, $height, $color);
        //干扰线
        for ($i = 0; $i < 3; $i++) {
            $color = imagecolorallocate($img, mt_rand(0, 255), mt_rand(0, 255), mt_rand(0, 255));
            @imageline($img, mt_rand(0, $width), mt_rand(0, $height), mt_rand(0, $width), mt_rand(0, $height), $color);
        }
        //画验证码
        $codeColor = imagecolorallocate($img, mt_rand(0, 200), mt_rand(0, 120), mt_rand(0, 120));
        @imagestring($img, 5, 5, 8, $code, $codeColor);
        //生成图像
        header("Content-type: Image/" . $type);
        $ImageFun = 'Image' . $type;
        $ImageFun($img);
        imagedestroy($img);
    }

    /**
     * 生成随机验证码
     *
     * @param int $length 生成长度
     * @return string
     */
    public static function randCode($length)
    {
        $string = "0123456789abcdefghijklmnopqrstuvwxyz";
        $code = '';
        for ($i = 0; $i < $length; $i++) {
            $code .= $string[mt_rand(0, strlen($string) - 1)];
        }
        return $code;
    }
}