明明已经安装了库确提示不找不到：

Fatal error: Uncaught Error: Class 'Gregwar\Captcha\CaptchaBuilder' not found in H:\composerDemo\index.php:5 Stack trace: #0 {main} thrown in H:\composerDemo\index.php on line 5

这是因为这依赖与autoload，所以要先把autoload.php导入：如下图:require_once __DIR__.'/vendor/autoload.php';

<?php
require_once __DIR__.'/vendor/autoload.php';
use Gregwar\Captcha\CaptchaBuilder;

$builder = new CaptchaBuilder;
$builder->build(120,30);
header("Content-type:image/png");
$builder->output();