Ah, so I can't have one picture for your catalog and one picture for Project Spark? I guess it will have to stay stretched then, as I want people to be able to use it in the display layer - and a big box around it is not ideal, it needs to be a cut out. Options for your app:
Keep the two images (catalog and icon) separate in the form. Both can be pre populated with the icon.png but you can change each independently. That way you can have a cut out icon for the assembly prop, and a more showcase style picture for the catalogue.