Are there any specific PHP functions or methods that can help improve the validation process for a captcha form?

When implementing a captcha form, it is important to validate the user input to ensure that it is correct. One way to improve the validation process is by using the PHP function `strtolower()` to convert the user input to lowercase before comparing it to the captcha code. This helps to make the validation case-insensitive, allowing users to enter the code in any combination of uppercase and lowercase letters.

// Get the user input from the form
$user_input = $_POST['captcha_input'];

// Get the captcha code stored in the session
$captcha_code = $_SESSION['captcha_code'];

// Convert the user input to lowercase
$user_input_lower = strtolower($user_input);

// Compare the lowercase user input to the captcha code
if ($user_input_lower == $captcha_code) {
    // Validation successful
    echo "Captcha validation successful!";
} else {
    // Validation failed
    echo "Captcha validation failed. Please try again.";
}