By "unmarked", do you mean "unsigned"?

Sometimes, there is information on the back of the picture. Can you see the back side? Maybe the back of the frame has boards to protect the backside of the picture. In that case, some disassenbly is required. If you are unfamilar with doing this, it is best you get professional help (provided the picture is worth it). It is a very nice frame, and there is the possibility that the frame is worth more than the picture, so be careful with it.

Can you tell us more about the picture, for example, is it oil on canvas, or something else? Experts on this forum can not provide much input until they know what they are dealing with.

Do you know how old it is? When was it put into the frame? Who was the first owner and when? This helps to associate a time period with the piece, or at least establish a minimum age.

It could be a reproduction on paper in a nice frame.

Great frame!!!