Completely agreed from a designer standpoint here, but for gameplay purposes it may become more distracting having larger images, not to mention the server load. I think these boxes can be upsized a little bit, but not by much; even an extra 8-10% would be satisfying without inhibiting gameplay.
For now, try designing your images with an easier-read colour gamut and more contrasting colours between the object in question and the background to make it easier to convey to players what you're trying to show.