How to use PHP to implement verification code and graphic recognition functions

How to use PHP to implement verification code and graphic recognition functions

Verification code (Captcha) is a common online verification mechanism used to confirm that the user is a real user. Not automated scripts or malware. Verification codes are often encountered during website registration, login, password reset and other operations. By identifying verification codes, we can prevent malicious attacks by robots and the sending of spam messages. This article will introduce how to use PHP to implement verification code and graphic recognition functions.

1. Generate verification code

First, we need to generate a verification code image for users to identify. Below is a simple PHP function that generates a verification code consisting of numbers and letters.

<?php
session_start();

function generateCaptcha($length = 4) {
    $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
    $captcha = '';
    for ($i = 0; $i < $length; $i++) {
        $captcha .= $chars[rand(0, strlen($chars) - 1)];
    }
    $_SESSION['captcha'] = $captcha; // 将验证码保存到 session 中
    return $captcha;
}

2. Display verification code image

After generating the verification code, we need to display it on the web page for users to enter. Below is a simple PHP script that generates a captcha image and displays it in the browser.

<?php
header("Content-type: image/png");

$captcha = generateCaptcha(); // 生成验证码

$width = 80; // 图像宽度
$height = 40; // 图像高度

$image = imagecreate($width, $height); // 创建图像

$background = imagecolorallocate($image, 255, 255, 255); // 设置图像背景色为白色
$textColor = imagecolorallocate($image, 0, 0, 0); // 设置文本颜色为黑色

// 将验证码绘制到图像上
imagestring($image, 5, 10, 12, $captcha, $textColor);

imagepng($image); // 输出图像
imagedestroy($image); // 销毁图像
?>

3. Verify the entered verification code

After the user sees the verification code image in the browser, they need to enter the verification code to continue the operation. Below is a simple PHP function to verify that the verification code entered by the user is correct.

<?php
session_start();

function validateCaptcha($input) {
    if (isset($_SESSION['captcha'])) {
        $captcha = $_SESSION['captcha'];
        unset($_SESSION['captcha']); // 验证码只能使用一次
        return strtolower($input) === strtolower($captcha);
    }
    return false;
}

4. Graphic recognition function

Sometimes, the verification code image will use some complex distortion, interference and other effects to prevent automatic recognition. In this case, we can use pattern recognition technology to automatically identify the verification code. Below is a simple PHP function that recognizes a CAPTCHA image.

<?php
function recognizeCaptcha($imagePath) {
    $image = imagecreatefrompng($imagePath);
    $width = imagesx($image);
    $height = imagesy($image);

    $captcha = '';
    for ($i = 0; $i < $width; $i++) {
        $color = imagecolorat($image, $i, $height / 2);
        $r = ($color >> 16) & 0xFF;
        $g = ($color >> 8) & 0xFF;
        $b = $color & 0xFF;
        $brightness = ($r + $g + $b) / (3 * 255);
        $captcha .= ($brightness < 0.5) ? '1' : '0';
    }

    imagedestroy($image);
    return $captcha;
}

The above is a simple example of using PHP to implement verification code and graphic recognition functions. By generating CAPTCHAs, displaying CAPTCHA images, validating user input and using pattern recognition technology, we can improve the security and user experience of our website. Of course, actual applications may involve more complex verification codes and pattern recognition algorithms, which need to be adjusted and optimized according to specific circumstances.

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