How to use PHP to implement a simple image verification code function

How to use PHP to implement a simple image verification code function

Image verification code is a common verification method used to verify user identity. When registering on a website, It is widely used in scenarios such as login and information submission. This article will introduce how to use the PHP programming language to implement a simple image verification code function and provide specific code examples.

1. Preparation
Before you start writing the image verification code function, you need to make sure that you have installed PHP and GD libraries. The GD library is an open source graphics library for processing image files. For installation methods, please refer to PHP official documentation or other related tutorials.

2. Generate verification code image
First, create a PHP file, such as captcha.php. In this file, we will generate a verification code image through the GD library and store the verification code value in the session for subsequent verification.

The following is a sample code to generate a verification code image:

<?php
session_start();

// 生成随机的四位验证码
$code = rand(1000, 9999);

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

// 创建一个宽度为120、高度为40的验证码图片
$image = imagecreatetruecolor(120, 40);

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

// 生成随机的干扰点
for ($i = 0; $i < 100; $i++) {
    $point_color = imagecolorallocate($image, rand(0, 255), rand(0, 255), rand(0, 255));
    imagesetpixel($image, rand(0, 120), rand(0, 40), $point_color);
}

// 设置验证码的字体颜色为黑色
$text_color = imagecolorallocate($image, 0, 0, 0);

// 在图片上绘制验证码
imagettftext($image, 20, 0, 30, 30, $text_color, 'path/to/font.ttf', $code);

// 发送图片到浏览器
header('Content-Type: image/png');
imagepng($image);
imagedestroy($image);
?>

3. Display the verification code image
In the location where the verification code is to be displayed, use the tag to reference captcha .php file, as shown below:

<img src="captcha.php" alt="验证码">

4. Verify user input
When the user submits the form, it is necessary to verify whether the verification code entered by the user is consistent with the verification code stored in the session. The following is a simple verification example code:

<?php
session_start();

if (isset($_POST['captcha'])) {
    $user_input = $_POST['captcha'];
    
    if ($user_input == $_SESSION['captcha_code']) {
        // 验证码正确，执行相应的操作
    } else {
        // 验证码错误，提示用户重新输入
    }
}
?>

The above code first checks whether the user has submitted the verification code field. The verification code entered by the user is then compared to the verification code stored in the session. If the verification code is correct, perform the corresponding operation; otherwise, prompt the user to re-enter the verification code.

Summary
This article introduces how to use PHP to implement a simple image verification code function. By using the GD library to generate a verification code image and storing the value of the verification code in the session, the basic verification code function is implemented. In actual use, it can be expanded and optimized according to needs, such as adding font styles, adding interference lines, etc.

Now, you can try to add the image verification code function to your website based on the code examples provided in this article!

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