What are the best practices for implementing captchas in PHP to prevent automated scripts from spamming forms?

To prevent automated scripts from spamming forms, implementing a captcha in PHP is a common solution. Captchas require users to complete a challenge to prove they are human, such as entering distorted text or solving a simple math problem. This can help reduce the amount of spam submissions and protect your forms from abuse.

// PHP Captcha Implementation
session_start();

// Generate a random captcha code
$captchaCode = substr(md5(rand()), 0, 6);
$_SESSION['captcha_code'] = $captchaCode;

// Display the captcha image on the form
echo '<img src="captcha.php" alt="Captcha Image">';

// Validate the captcha code on form submission
if(isset($_POST['submit'])){
    if($_POST['captcha'] == $_SESSION['captcha_code']){
        // Captcha code is correct, process form submission
        // Add your form processing logic here
    } else {
        // Captcha code is incorrect, display error message
        echo 'Captcha code is incorrect. Please try again.';
    }
}