Fatal error: Class'think\captcha' not found

The following is the controller code:

use think\captcha\Captcha;
 
class Index extends Admin
{
 
    public function loginAction()
    {
        $captcha = new Captcha();
        $a= $captcha->entry();
        echo $a;exit;

Thinkphp root directory, right-click here to open the command line and execute the following command.

composer require topthink/think-captcha The
official version 5.0 extension library version number is 1.*, and the 2.0 version is dedicated to ThinkPHP5.1.

Simple usage of verification code
Some common usages are defined in the extension package for easy use. The following examples illustrate

Note: URL routing needs to be turned on.

Display of verification code in template

<div>{:captcha_img()}</div>
or

<div><img src="{:captcha_src()}" alt="captcha" /></div>