PHP Generates Graphic Verification Code

Here's a simple tutorial on how to generate a graphic verification code, often known as a CAPTCHA, using PHP.

Create a new PHP file (let's call it captcha.php) and open it in your favorite text editor.
First, start a session. It's necessary because we'll store the CAPTCHA text in a session variable.

<?php
session_start();
?>

Then, define the basic parameters for your CAPTCHA image:

<?php
$width = 200;
$height = 60;
$font_size = 20;
$total_characters = 5;

Next, create an image using the imagecreatetruecolor() function, and define the color for the background and the text:

$image = imagecreatetruecolor($width, $height);

$background_color = imagecolorallocate($image, 255, 255, 255); // white
$text_color = imagecolorallocate($image, 0, 0, 0); // black

imagefilledrectangle($image, 0, 0, $width, $height, $background_color);

Now, generate a random string and draw it on the image. Here we are using a simple alphanumeric string:

$characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
$random_string = '';
for ($i = 0; $i < $total_characters; $i++) {
    $random_string .= $characters[rand(0, strlen($characters) - 1)];
}

// Save the CAPTCHA string into a session variable
$_SESSION['captcha_text'] = $random_string;

$font = 'arial.ttf'; // Path to your font file

imagettftext($image, $font_size, 0, 15, 30, $text_color, $font, $random_string);

Remember, the path to the font file is relative to the script generating the image.

Finally, output the image with proper headers:

header('Content-type: image/png');
imagepng($image);
imagedestroy($image);

Put all together:

<?php
session_start();

$width = 200;
$height = 60;
$font_size = 20;
$total_characters = 5;

$image = imagecreatetruecolor($width, $height);

$background_color = imagecolorallocate($image, 255, 255, 255); // white
$text_color = imagecolorallocate($image, 0, 0, 0); // black

imagefilledrectangle($image, 0, 0, $width, $height, $background_color);

$characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
$random_string = '';
for ($i = 0; $i < $total_characters; $i++) {
    $random_string .= $characters[rand(0, strlen($characters) - 1)];
}

$_SESSION['captcha_text'] = $random_string;

$font = 'arial.ttf'; 

imagettftext($image, $font_size, 0, 15, 30, $text_color, $font, $random_string);

header('Content-type: image/png');
imagepng($image);
imagedestroy($image);
?>

You can then include this CAPTCHA image in your HTML form by using an image tag:

<img src="captcha.php" />

And when the form is submitted, you can check the user's input against the $_SESSION['captcha_text'] value to verify if they entered the correct CAPTCHA.

Creating graphic verification codes in PHP:

Use the GD library to generate random verification codes.

<?php
session_start();

$verificationCode = generateVerificationCode();
$_SESSION['verification_code'] = $verificationCode;

$image = createCaptchaImage($verificationCode);
header('Content-Type: image/png');
imagepng($image);
imagedestroy($image);

function generateVerificationCode($length = 6) {
    $characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
    $code = '';
    for ($i = 0; $i < $length; $i++) {
        $code .= $characters[rand(0, strlen($characters) - 1)];
    }
    return $code;
}

function createCaptchaImage($text) {
    $imageWidth = 150;
    $imageHeight = 50;
    $image = imagecreate($imageWidth, $imageHeight);
    $backgroundColor = imagecolorallocate($image, 255, 255, 255);
    $textColor = imagecolorallocate($image, 0, 0, 0);

    // Add noise or distortion effects if desired

    imagettftext($image, 20, 0, 10, 30, $textColor, 'arial.ttf', $text);
    return $image;
}

Using GD library to generate captcha in PHP:

Utilize the GD library functions to create captcha images.

<?php
$verificationCode = generateVerificationCode();
$image = createCaptchaImage($verificationCode);
header('Content-Type: image/png');
imagepng($image);
imagedestroy($image);

// Functions from the previous example

Adding security with graphic verification in PHP forms:

Implement a captcha system to enhance form security.

<?php
session_start();

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $userInput = $_POST['captcha'];
    $verificationCode = $_SESSION['verification_code'];

    if ($userInput === $verificationCode) {
        // Captcha verification successful
    } else {
        // Captcha verification failed
    }
}

Customizing and styling captcha images in PHP:

Adjust colors, fonts, and other parameters for customization.

<?php
function createCaptchaImage($text) {
    $imageWidth = 150;
    $imageHeight = 50;
    $image = imagecreate($imageWidth, $imageHeight);
    $backgroundColor = imagecolorallocate($image, 200, 220, 230);
    $textColor = imagecolorallocate($image, 0, 0, 0);

    imagettftext($image, 20, 0, 10, 30, $textColor, 'arial.ttf', $text);
    return $image;
}

PHP captcha code examples:

Examples of using captcha in PHP for form protection.

<?php
// Example HTML form
?>
<form method="post" action="process_form.php">
    <label for="captcha">Enter the code:</label>
    <img src="captcha.php" alt="Captcha Image">
    <input type="text" name="captcha" required>
    <button type="submit">Submit</button>
</form>
<?php
// PHP processing code

Refreshing or reloading captcha images in PHP:

Allow users to refresh the captcha if needed.

<?php
session_start();

if ($_SERVER['REQUEST_METHOD'] === 'GET') {
    $verificationCode = generateVerificationCode();
    $_SESSION['verification_code'] = $verificationCode;

    $image = createCaptchaImage($verificationCode);
    header('Content-Type: image/png');
    imagepng($image);
    imagedestroy($image);
}

Integrating captcha with user registration in PHP:

Enhance user registration with captcha verification.

<?php
session_start();

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $userInput = $_POST['captcha'];
    $verificationCode = $_SESSION['verification_code'];

    if ($userInput === $verificationCode) {
        // Captcha verification successful, process user registration
    } else {
        // Captcha verification failed
        echo "Captcha verification failed.";
    }
}

Verifying user input with PHP captcha codes:

Validate user input against the captcha code.

<?php
session_start();

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $userInput = $_POST['captcha'];
    $verificationCode = $_SESSION['verification_code'];

    if ($userInput === $verificationCode) {
        // Captcha verification successful
    } else {
        // Captcha verification failed
    }
}

Anti-bot techniques using graphic verification in PHP:

Use captcha to prevent automated bot submissions.

<?php
// Add captcha to forms to prevent bot submissions
// Example HTML form
?>
<form method="post" action="process_form.php">
    <label for="captcha">Enter the code:</label>
    <img src="captcha.php" alt="Captcha Image">
    <input type="text" name="captcha" required>
    <button type="submit">Submit</button>
</form>
<?php
// PHP processing code