What are some common methods for verifying user registration in PHP applications?

// Generate a unique verification token
$verification_token = md5(uniqid(rand(), true));

// Save the token in the database along with the user's email
$query = "INSERT INTO users (email, verification_token) VALUES ('$email', '$verification_token')";
$result = mysqli_query($conn, $query);

// Send a verification email to the user
$to = $email;
$subject = 'Verify Your Email Address';
$message = 'Click the following link to verify your email address: http://example.com/verify.php?token=' . $verification_token;
$headers = 'From: admin@example.com';
mail($to, $subject, $message, $headers);
```

Another method is to use a CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) to prevent automated bots from registering fake accounts.

```php
// Verify CAPTCHA response
$secret_key = 'YOUR_SECRET_KEY';
$captcha_response = $_POST['g-recaptcha-response'];

$response = file_get_contents("https://www.google.com/recaptcha/api/siteverify?secret=$secret_key&response=$captcha_response");
$response_keys = json_decode($response, true);

if(intval($response_keys["success"]) !== 1) {
    // CAPTCHA verification failed
    die('CAPTCHA verification failed. Please try again.');
}