如何用PHP制作验证码？中文验证码生成方法

<?php
session_start();
header('Content-Type: image/png');

$width = 120;
$height = 40;
$image = imagecreatetruecolor($width, $height);

$bgColor = imagecolorallocate($image, 255, 255, 255);
imagefill($image, 0, 0, $bgColor);

$code = '';
$chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
for ($i = 0; $i < 4; $i++) {
    $code .= $chars[rand(0, strlen($chars) - 1)];
}
$_SESSION['captcha'] = $code;

$textColor = imagecolorallocate($image, 0, 0, 0);
imagestring($image, 5, 30, 10, $code, $textColor);

// 加点干扰线或点
for ($i = 0; $i < 5; $i++) {
    imageline($image, rand(0, $width), rand(0, $height), rand(0, $width), rand(0, $height), imagecolorallocate($image, 150, 150, 150));
}

imagepng($image);
imagedestroy($image);

<?php
session_start();
header('Content-Type: image/png');

$width = 150;
$height = 50;
$image = imagecreatetruecolor($width, $height);

$bgColor = imagecolorallocate($image, 255, 255, 255);
imagefill($image, 0, 0, $bgColor);

// 常见中文字符集
$chineseChars = '你好世界欢迎测试验证码功能';
$code = '';
for ($i = 0; $i < 4; $i++) {
    $code .= $chineseChars[rand(0, mb_strlen($chineseChars, 'UTF-8') - 1)];
}
$_SESSION['captcha'] = $code;

$fontFile = 'simsun.ttc'; // 确保字体文件路径正确
$fontSize = 20;
$textColor = imagecolorallocate($image, 0, 0, 0);

// 随机位置绘制每个字
$x = 20;
for ($i = 0; $i < strlen($code); $i++) {
    $char = mb_substr($code, $i, 1, 'UTF-8');
    imagettftext($image, $fontSize, 0, $x, 30, $textColor, $fontFile, $char);
    $x += 30;
}

// 添加干扰线
for ($i = 0; $i < 5; $i++) {
    imageline($image, rand(0, $width), rand(0, $height), rand(0, $width), rand(0, $height), imagecolorallocate($image, 150, 150, 150));
}

imagepng($image);
imagedestroy($image);

if (strtolower($_POST['user_input']) == strtolower($_SESSION['captcha'])) {
    echo '验证码正确';
} else {
    echo '验证码错误';
}