Unfortunately not for cover images.
What would a "cover images" variable return? A list of file names? A list of file ids?
Neither would be usable for a data-driven category that produces what you have in mind, I suspect.
(For correctness one should then not allow a cover image to be associated with more than one event.)
That would be quite limiting. I really enjoy being able to 'depict' an event with multiple images.
I guess you are trying to create some sort of event timeline
outside the Event View, right? By somehow using cover images in a category or whatever.
And you can, by just assigning the files you use for your events to a category. I don't see a need to automate this in any way. Most users get by with maybe 100 events, adding a few events per month. Very doable to assign the cover files to a category of your choice, to produce whatever you have in mind.
I use the Event View to see all my events, and their cover files, aligned long the timeline like pearls...
I use the filter dialog to get a compressed list of events if needed and to control which events I want to see. Disabling the files calendar produces a very compact view, allowing me to see the events of many months or even years on a single screen page.