The reason for the inconsistency is becuase these items were moved from many other categories. And no one really cared about those entries before, that is why it is a mess.
Front/back is how it should be, as you put it.
There is no media (what third image is for) so that image spot should not be used at all. It is important that the third spot only be used for media, no matter what the type of item is. It is for future programming reasons why it shouldn't be repurposed for other item types that do not contain media.