It may well be a hand painted porcelain plaque that is a copy of the Kray painting. Some of these porcelain copies are quite valuable. Check it over w a loupe to see if hand painted. Also Remove all the paper from the back and look for a Royal Vienna Porcelain Mark. The gallery label on yours is associated with some Royal Vienna stuff. Be forewarned that Royal Vienna is a bit of a rabbit hole to go down - lots of different marks, different companies, different artists etc. BUT I think it’s worth it in this case.