Small Oval Hunt Scene, All Metal, High Relief: How Made & When?

I have a strong sense that the process involves electro-deposition. I've not seen the like of this in all my years of collecting; that's why I had to have it.
The frame is ~6 1/4" X ~5 1/4"; the brass bezel is ~4" X 3". The image relief is maybe a bit over 1/4" deep.
There are 3 mounted individuals, 2 men an' a woman; there are 2 men without mounts; one kneeling near a dog, the other standing with a long firearm, barrel in hand. 2 other dogs are at lower right.
The group appears just outside a gate, in a forest setting. All 4 men appear to be wearing tri-cornered hats.
There is a zinc-like cast to the scene, but copper shows through on high points, probably due to enthusiastic scrubbing with metal polish, some remnants of which appear in a few hidden places.
I'm hoping some of you with more experience in unusual art forms will be able to tell me what this piece is an example of, in terms of the process used to create the scene...and whether the grouping is a copy of some other, more famous medium. Thanks for lookin'!