Rare Antique Micro Mosaic Brooch

Haven't installed any new jewelry in a long time. But now I have in my large collection of this kind of jewelry a special micro mosaic brooch again. During collecting I have come across many different common images such as birds, flowers, etc. But never an image like this. After much research I suspect this is an image of the last Venice Doge Italy Lodovico Giovanni Manin ( 14.05.1725 – 24.10.1802) He was a Venetian politician and the last Doge of Venice. He was forced to abdicate by Napoleon Bonaparte in 1797.

This brooch is gold plated on hallmarked 800 silver what has been implemented on the back of the brooch as you can see on image 4.
All in all, a very special brooch without only one single tesserae missing.
The brooch has a diameter from 3 cm. and weight: 8 gr.

My question to you: "Have you seen this kind of image before? And do you think this could be an image of someone else? And could this brooch be rare, given the above information?