What is a picture frame stage?

A picture frame stage is a type of stage that consists of a rectangular frame with a flat background, which is often used for displaying items such as paintings, photographs, or other artworks. The frame can be made of various materials, such as wood, metal, or plastic, and it can be hung on a wall, placed on a tabletop, or used in other ways to display items. Picture frame stages are sometimes called shadowbox stages because they can be used to create a three-dimensional effect by placing the displayed item inside the frame.