How to use PHP to implement human-machine verification code

Human-machine verification code is a commonly used form of verification code, which can effectively prevent malicious robot attacks and malicious registration. As a server-side language, PHP is very suitable for implementing human-machine verification code functions. In this article, we will introduce how to implement human-machine verification code using PHP.

1. Generate verification code image
   First, we need to generate a verification code image. This process can be achieved by using the GD library. The GD library is an open source image processing library that can be used to generate and manipulate various types of images. In PHP, you can use it by installing the GD extension.

The following is a code example for generating a verification code image:

<?php
session_start();
$code = rand(1000, 9999);
$_SESSION["code"] = $code;
$width = 100;
$height = 50;
$image = imagecreatetruecolor($width, $height);
$textColor = imagecolorallocate($image, 0, 0, 0); //设置文本颜色
$bgColor = imagecolorallocate($image, 255, 255, 255); //设置背景颜色
imagefilledrectangle($image, 0, 0, $width, $height, $bgColor); //绘制矩形背景

//绘制验证码字符串
$font = 'arial.ttf'; //字体
$fontSize = 24; //字体大小
$x = 20; //x轴位置
$y = 30; //y轴位置
for ($i = 0; $i < 4; $i++) {
    $char = substr(str_shuffle("ABCDEFGHJKMNPQRSTUVWXYZ23456789"), 0, 1);
    imagettftext($image, $fontSize, rand(-15, 15), $x, $y, $textColor, $font, $char);
    $x += 20;
}

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

This code will generate a verification code image on the server side and output it to the browser for display.

2. Verify user input
   Next, we need to verify whether the user input is correct. When generating the verification code, we have saved the verification code in the Session. Therefore, after the user submits their input, we can compare the verification code entered by the user with the verification code saved in the Session.

The following is a code example to verify user input:

<?php
session_start();
if($_POST["code"] != $_SESSION["code"]) {
    echo "验证码输入错误";
} else {
    echo "验证码输入正确";
}
?>

This code will verify whether the verification code submitted by the user is the same as the verification code saved in the Session. If they are not the same, an error message will be output; if they are the same, it means the user input is correct.

3. Embedded into the form
   Finally, we need to embed the human-machine verification code into the form. In order to prevent malicious attackers from directly submitting the form without entering the verification code, we need to display the verification code generation script and the form on the same page, and verify it after submission.

The following is a code example for embedding the human-machine verification code into the form:

<form method="post" action="verify.php">
    <p>用户名：</p>
    <input type="text" name="username">
    <p>密码：</p>
    <input type="password" name="password">
    <p>验证码：</p>
    <input type="text" name="code">
    <img src="code.php" alt="验证码">
    <input type="submit" value="提交">
</form>

This code will add an image to the form to display the verification code. Users need to enter the verification code shown in the image to submit the form. After clicking the submit button, the form will jump to the verification script code and perform verification.

Summary
This article introduces how to use PHP to implement human-machine verification code. By generating a verification code image and saving it to the Session, malicious attacks and registration can be effectively prevented. Embedding human-machine verification codes in forms can effectively improve website security and user experience.

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