In order to do this, you would have to practically build an embedded Ultima Online client into your shard.
You will have to write an isometric grid algorithm to simulate the UO client's display as seen when logged in with the real thing.
This client would have to be able to locate, find and generate images based on everything it can 'see' on this isometric grid.
When the grid is populated/generated, you would then have to draw your screenshot image from application memory to a recognisable image file format.
In short, it would be much easier to just log-in an actual UO client and find a 3rd party tool that takes screenshots of the game window at specified intervals/times, but simulating the display window of the game client in RunUO is a task where the rewards are far outweighed by the work put in. You'd have to find a bigger reason than just taking 'screenshots of random places in game' to gain interest in such a project.
I've tried to do this all myself in the past when I released a (now abandoned) project that delivered live web content from RunUO - the intention was to generate an isometric view of any point in the game that the browser requested - but the overhead was insane and it didn't work out.