Are there any best practices for generating and validating CAPTCHA codes in PHP?

Generating and validating CAPTCHA codes in PHP is essential for preventing automated bots from submitting forms on websites. To ensure security, it is recommended to use a combination of random characters and mathematical operations to create a CAPTCHA code. When validating the code, compare the user input with the generated CAPTCHA code to determine if it is correct. 

// Generate a random CAPTCHA code
$captcha_code = substr(md5(uniqid(mt_rand(), true)), 0, 6);

// Store the CAPTCHA code in a session variable
session_start();
$_SESSION['captcha_code'] = $captcha_code;

// Display the CAPTCHA image to the user
$im = imagecreatetruecolor(100, 30);
$bg_color = imagecolorallocate($im, 255, 255, 255);
$text_color = imagecolorallocate($im, 0, 0, 0);
imagestring($im, 5, 5, 5, $captcha_code, $text_color);
header('Content-type: image/png');
imagepng($im);
imagedestroy($im);

// Validate the user input
if(isset($_POST['captcha_input'])) {
    if($_POST['captcha_input'] == $_SESSION['captcha_code']) {
        // CAPTCHA code is valid
        echo "CAPTCHA code is correct!";
    } else {
        // CAPTCHA code is invalid
        echo "CAPTCHA code is incorrect!";
    }
}

Keywords

CAPTCHA PHP validation generation security

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