https://github.com/bazzel/ember-workshop, tag 4.0.0

form.hbs

<div class='form-group'>
  {{#if image}}
    <img {{bind-attr src=image}}/>
    <button type='button' class='remove pull-right'>Remove</button>
  {{else}}
    <img src='http://placehold.it/320x150&text=No image'>
  {{/if}}
  <div class='file'>
    Browse...<input type='file' accept='image/*'>
  </div>
</div>

upload-file.js

import Ember from 'ember';

export default Ember.TextField.extend({
  type: 'file',
  change: function (e) {
    var reader = new FileReader(),
        _this = this;
        
    reader.onload = function (e) {
      var fileToUpload = e.srcElement.result;
      
      Ember.run(function() {
        _this.set('file', fileToUpload);
      });
    };
    return reader.readAsDataURL(e.target.files[0]);
  }
});