How to setup a RequestHandler for images with VaadinServlet

I want to have a RequestHandler to be able to dynamically create images at say myDomain/images/id8938748.jpg and at the same handle all other traffic through the standard VaadinServlet. To do this I understand that I need to put the RequestHandler in the VaadinServlet as explained here by extending it such as:

public class MyCustomServlet extends VaadinServlet 
{
        @Override
        protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
        {
            getService().addSessionInitListener(new SessionInitListener() 
            {
                @Override
                public void sessionInit(SessionInitEvent event) throws ServiceException 
                {
                    event.getSession().addRequestHandler(myCustomRequestHandlerForImages);
                }
            });
        }
}

My problem is how do you register the new MyCustomServlet? I looked at doing it in the web.xml but I just can't seem to get it right.

My RequestHandler is simply:

@Override
public boolean handleRequest(VaadinSession session, VaadinRequest request, VaadinResponse response) throws IOException 
{
    System.out.println("Test it's being called");
}

For the web.xml I have:

<servlet>
    <servlet-name>MyCustomVaadinServlet</servlet-name>
    <servlet-class>
        com.test.MyCustomVaadinServlet
    </servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>MyCustomVaadinServlet</servlet-name>
    <url-pattern>/images/*</url-pattern>
</servlet-mapping>

I then have the other Servlet defined in the UI code with annotations:

public class MyUI extends UI
{
  @WebServlet(value = "/*", asyncSupported = true)
  @VaadinServletConfiguration(productionMode = false, ui = MyUI.class, widgetset = "com.MyWidgetSet")
    public static class Servlet extends VaadinServlet 
  {
  }
  ...
}

When I call domain itself it all works as expected and my Vaadin application works. But when I call domain/images or domain/images/randomText I get an empty page and the System.out.println statements are NOT outputted. Basically the RequestHandler is NOT called.

I have also tried things like mapping to /images/* and /app/* but that didn't make any difference...