Here's an idea I came up with while browsing through several images of many sizes. The advantage of only zooming small images is to keep small images easily viewable (in a large size), but it'll also keep text or other small details on large images to be visible (instead of shrinking the image where you can't see them or make them out clearly).
Right now, all I can do is set it to "Fit Image to Window/Desktop, all" and then manually zoom in the images that are so big that their text/detail is lost.
This is a pretty simplistic suggestion, so that's really it
