There are quite a few different scenarios that make it not so meaningful. e.g. multiple photos; photos not hosted on Rolia, etc.
-sailor(Ocean & Mountain);
2019-7-6(#675269@6)
Logically a photo is not limited to one category. The same instance of photo (i.e. with the same URL0 can be displayed in many different categories.
-system;
2019-7-27(#675289@6)