I’m sorry if I sounded harsh, but as Sam mentioned the changes needed to display pictures @ 4k require modifying the system as well as kodi and since there has not been a high demand for such feature it’s reasonable to ask users to get their hands dirty if they want to test that first.
It’s the same thing I did and I’m still doing to make moonlight work on the Vero 4k, Sam provided me with instructions and hints on how to compile it and I did.
Anyway, as stated in other similar threads, I have viewed 4k pictures on my tv before, but I was and am satisfied with the downscaling (I used the google drive addon to view google photos pictures stored on it).