Well, the widget is not meant to display images the way the traditional image viewer does, it is intended to display images based on a (calculated) URL, in contrast to the traditional viewer which display images stored in your domain model. (The image viewer documentation describes however how the URL of an stored image can be retrieved if you really want to).
Note that the documentation of each image can be found in appstore.mendix.com > your widget > read more > documentation. (or click here)
Thanks for the info!
Where can I add a feature request for scaling of images in the traditional image viewer?