php网页显示验证码

<?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;
}

// 创建图像
$image = imagecreatetruecolor(100, 30);
$backgroundColor = imagecolorallocate($image, 255, 255, 255);
$textColor = imagecolorallocate($image, 0, 0, 0);

imagefilledrectangle($image, 0, 0, 100, 30, $backgroundColor);

// 生成验证码字符串并保存到session
$randomString = generateRandomString();
$_SESSION['captcha'] = $randomString;

// 将字符串写入图像
imagestring($image, 5, 20, 8, $randomString, $textColor);

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