会话始终存储以前的值

Question

我正在开发一个电子邮件发送表单。它有一个验证码安全图像。当我刷新图像以加载新的验证码时，它总是存储先前的会话值。它永远不会存储正确的。

但是在我的localhost中它运行正常。非常感谢你。

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++;
        }

        $_SESSION['securitycode'] = $code;

        return $code;
    }

    function CaptchaSecurityImages($width='120',$height='40',$characters='6') {
        $code = $this->generateCode($characters);
        /* font size will be 75% of the image height */
        $_SESSION['securitycode'] = $code;      
        $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);


    }

}

这是我用来生成验证码的类。