php如何编写验证码

<?php
session_start();

// 生成随机字符串
function generateRandomString($length = 6) {
    $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $charactersLength = strlen($characters);
    $randomString = '';
    for ($i = 0; $i < $length; $i++) {
        $randomString .= $characters[rand(0, $charactersLength - 1)];
    }
    return $randomString;
}

// 创建验证码图像
function createCaptchaImage($code) {
    $width = 150;
    $height = 50;
    $image = imagecreatetruecolor($width, $height);
    $backgroundColor = imagecolorallocate($image, 255, 255, 255);
    imagefill($image, 0, 0, $backgroundColor);

    // 添加干扰线
    for ($i = 0; $i < 5; $i++) {
        $color = imagecolorallocate($image, rand(0, 255), rand(0, 255), rand(0, 255));
        imageline($image, rand(0, $width), rand(0, $height), rand(0, $width), rand(0, $height), $color);
    }

    // 添加验证码文字
    $textColor = imagecolorallocate($image, 0, 0, 0);
    imagettftext($image, 20, 0, 30, 30, $textColor, 'arial.ttf', $code);

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

// 生成验证码并保存到session
$code = generateRandomString();
$_SESSION['captcha'] = $code;

createCaptchaImage($code);
?>