Exclude files from broccoli Ember 2.0

Hi im kind of new to ember, im looking for a way to tell broccoli not to include my img/ directory, i want to include some default images there which ill be programatically adding to the app

<img src='{{model.picture}}'/>

And i can see them ok in development but not in production since the name has a hash attaches due to brocolli task, how do i configure my BrocFile to exclude files in the directory i have checked the documentation here

http://ift.tt/1VQxdgP

but i cant figure out where in my brocfile im expected to add that.

part of my brocfile

var EmberApp = require('ember-cli/lib/broccoli/ember-app');
    var app = new EmberApp({
        modals: {
            layout: true,
            style: true,
            animation: 'scale'
        }
    });



    app.import({
        production: 'bower_components/raygun4js/dist/raygun.js'
    });
    app.import('bower_components/lodash/lodash.js');