HELP! What was this plaque used for?

Several years ago, I picked up this brown and white enamel plaque that has a portrait of a woman on it.  When I purchased it, I was told by the dealer that it was a decoration off of the front of a stove that was made around the late 1800’s to the early 1900’s.

The dealer also said that they thought it was enameled copper.

Ever since the day I got it, I have been poking around to see what exactly it is.  The first thing that I ran across was a picture of Queen Elizabeth during her Diamond Jubilee of 1897.  The picture was pretty close to the image on the front of the plaque.

Another thing that really threw me for a loop was that I saw another listing on the internet that said these plaques were used on a front door of a house.

Is it really a decoration for a stove or a door?  Was it really made of copper?  If it was off of a stove, what brand was it on?  If you know what this is, feel free to drop me a line.  I would love to know is what this was used for.