phpcms 验证码问题

// 示例代码：生成图像验证码
session_start();
header('Content-type: image/png');

$width = 100;
$height = 30;
$image = imagecreate($width, $height);

$bgColor = imagecolorallocate($image, 255, 255, 255);
$textColor = imagecolorallocate($image, 0, 0, 0);

$code = rand(1000, 9999);
$_SESSION['captcha'] = $code;

imagestring($image, 5, 30, 8, $code, $textColor);

imagepng($image);
imagedestroy($image);

// 示例代码：验证验证码
session_start();

if ($_POST['captcha'] == $_SESSION['captcha']) {
    echo '验证码正确';
} else {
    echo '验证码错误';
}

<!-- 示例代码：刷新验证码按钮 -->
<button onclick="refreshCaptcha()">刷新验证码</button>

<script>
function refreshCaptcha() {
    var img = document.getElementById('captcha');
    img.src = 'captcha.php?' + new Date().getTime();
}
</script>