Frame and Mask acts just like a custom photoframe. You can frame up all your images with a single frame image without having to change the images manually in an editor. The mask image provides transparency/translucency information, so the Slideshow knows where to show the frame and where to show the image. Opaque material and translucent material, like glass, can be simulated using this feature.

The Frame and Mask is a powerful combination that allows you to create any kind of photoframe effect imaginable.