I guess arb meant your own connection with this portrait. How you came by it. A painting bought at a Florida jumble sale has a different history from one found at a Bulgarian church. Auctioneers always ask where paintings come from. Knowledge and a connaisseur's eye is usually not enough. Art is a 'mer ŕ boire'. You need clues.
No reliable data. I had hope that someone could read the inscription. Or someone will recognize the monogram. Perhaps someone has another work by this artist. If I had an inventory number and a document from the museum, I would not ask a question here.
The inscription might have to do with the frame only: 3 cm Einlage feld?Regards, Vietato
That would make sense indeed, Vietato. Or: 3cm Einlage Gold. That would be an instruction to insert a 3cm golden inlay. Which would point at a German origin. Which would coincide with the lettering. Which would narrow down the hundreds of LK's in the world of art to a few dozen. Which would lead to Ludwig Anton Maria KRIEBEL (1823-1890) known as Ludwig Kriebel.