Missing controller

You are seeing this error because controller ImgController could not be found.

Notice: this error is being rendered by the app/views/errors/missing_controller.thtml view file, a user-customizable error page for handling invalid controller dispatches.

Fatal: Unable to load controller ImgController

Fatal: Create Class:

<?php
class ImgController extends AppController
{
    var $name = 'Img';
}
?>

in file : app/controllers/img_controller.php