Easiest way to transfer custom photos between game saves?

The best way to test this out in your game. Keep the original game save, but then do what you are asking about. This is what I do when I'm not sure of something. The only thing that might happen if the painting was done by a certain sim, who painted it will be lost, their name not the painting. But then again I've seen the game lose that information in the same game save, which I really wished there was a way I could stop that.