Is there a equivalent to $app->pass() in V3?

I am trying to implement visualCaptcha in V3. If you go to the link you’ll see the developers of visual captcha has given example with slim v2. While I have implemented some parts of it well I am having some difficultly translating some of the code so v3 understands it.

Any help would be appreciated.

To add extra context I am trying to implement the function

   $app->get( '/image/:index', function( $index ) use( $app ) {
        $captcha = new \visualCaptcha\Captcha( $app->session );
        if ( ! $captcha->streamImage(
                     $app->request->params( 'retina' )
             ) ) {
      } );

Whereas I have currently,


        $this->app->get( '/image/{index}', 'VisualCaptchaController:index' );


      public function index ($request, $response, $args) { 
           $captcha = new \visualCaptcha\Captcha ($this->getCaptchaSession());
           $captcha->streamImage ($response, $args['index'], $this->container->getParam('retina'));