Error ImgController could not be found.
In the case you tried to access a plugin controller make sure you added it to your composer file or you use the autoload option for the plugin.
Suggestion Create the class ImgController below in file: src/Controller/ImgController.php
<?php
namespace App\Controller;
use App\Controller\AppController;
class ImgController extends AppController
{
}
If you want to customize this error message, create templates/Error/missing_controller.php