How to create dynamic image verification code using PHP and GD library-PHP Tutorial-php.cn

How to create dynamic image verification code using PHP and GD library

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Release： 2023-07-12 08:42:01

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How to create a dynamic image verification code using PHP and GD library

In web applications, in order to prevent robots and malicious attackers from automating operations, verification codes are often used to require users to enter a verification code to confirm. its identity. By using PHP and GD library, we can easily create dynamic image verification codes.

The GD library is an extension library for PHP that provides some functions for processing images. In this article, we will use the functions of the GD library to generate an image containing random characters and present it to the user as a verification code.

Step 1: Create a simple PHP web page

First, we need to create a simple PHP web page to present our dynamic image verification code. Create a file called index.php and copy the following code into the file:

<!DOCTYPE html>
<html>
<head>
    <title>动态图片验证码</title>
</head>
<body>
    <h1>动态图片验证码</h1>
    <img src="captcha.php" alt="验证码">
    <br>
    <a href="">换一个验证码</a>
</body>
</html>

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In this simple HTML page, we have created a title and an image element that displays the verification code. We set captcha.php for the src attribute of the image, we will later generate and render the image in this file.

Step Two: Create the captcha.php file

Now, we need to create a file called captcha.php and copy the following code into the file:

<?php
// 启动会话
session_start();

// 创建图像宽度和高度
$width = 200;
$height = 50;

// 创建一个空的图像
$image = imagecreatetruecolor($width, $height);

// 设置背景颜色
$bg_color = imagecolorallocate($image, 255, 255, 255);
imagefill($image, 0, 0, $bg_color);

// 生成随机的验证码
$characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
$length = mt_rand(4, 6);
$code = '';
for ($i = 0; $i < $length; $i++) {
    $code .= $characters[mt_rand(0, strlen($characters) - 1)];
}

// 将验证码存储在会话中
$_SESSION['captcha_code'] = $code;

// 设置文本颜色
$text_color = imagecolorallocate($image, 0, 0, 0);

// 在图像中绘制验证码
$font = __DIR__ . '/arial.ttf';
imagettftext($image, 30, 0, 10, 40, $text_color, $font, $code);

// 发送图像头信息
header('Content-Type: image/png');

// 将图像呈现给用户
imagepng($image);
imagedestroy($image);
?>

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In this PHP file, we first start the session so that the verification code can be stored and accessed. We then created an empty image with a specified width and height, and set the background color to white. Next, we generate a verification code containing random characters and store it in the session.

Then, we set the text color to black and draw the text of the verification code on the image using the selected font. Finally, we send the image header information and present the image to the user.

Step 3: Test and use the verification code

Now, we can open the index.php file in the browser and view the generated verification code. Each time the page is refreshed, a different verification code is generated.

In the form, we can verify the user's identity by checking whether the verification code entered by the user matches the verification code stored in the session.

We can use the following code to check the correctness of the verification code:

session_start();

if (isset($_POST['submit'])) {
    if ($_POST['captcha'] == $_SESSION['captcha_code']) {
        // 验证码正确，执行所需操作
    } else {
        echo '验证码错误！';
    }
}

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Here we assume that the content of this article does not include the form part and only demonstrates how to verify the correctness of the verification code.

By using PHP and GD library, we can easily create dynamic image verification codes to protect our web applications. These verification codes play an important role in identifying real users and preventing automated attacks.

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