Compositional frames are frames combining pictures from different sources into a single image.

A photo frame is the entire rectangle that contains a scene. Within it it may create an additional compositional frame — certain elements that surround the subject. Serving as the outer rim of the composition, a compositional frame keeps viewers’ eyes from leaving the image and directs them to the scene’s important components. Compositional frame can be made from almost anything within the scene.

When composing an image using elements in the foreground as compositional framing elements, the purpose is to seal off the edges of the image with elements that exist in a natural way that doesn't seem too obvious or forced.