phpcms 注册验证码

<?php
session_start();

// 生成验证码
if (empty($_SESSION['captcha'])) {
    $_SESSION['captcha'] = substr(md5(uniqid(mt_rand(), true)), 0, 5);
}

// 验证验证码
if ($_POST['captcha'] != $_SESSION['captcha']) {
    echo "验证码错误";
    exit;
}

echo "注册成功";
?>

<!DOCTYPE html>
<html>
<head>
    <title>注册页面</title>
</head>
<body>
    <form method="post">
        <label for="username">用户名:</label>
        <input type="text" id="username" name="username"><br><br>
        <label for="password">密码:</label>
        <input type="password" id="password" name="password"><br><br>
        <label for="captcha">验证码:</label>
        <input type="text" id="captcha" name="captcha">
        <img src="captcha.php" alt="验证码"><br><br>
        <input type="submit" value="注册">
    </form>
</body>
</html>