Chapter 2 of the book is all about Image Matting, the separation of a natural image into foreground and background elements. It’s not quite like putting a jigsaw puzzle together, since the “pieces” are fuzzy (e.g., background partially shows through an actor’s wispy hair). The matting problem gets its name from the way scenes in old-school Hollywood movies were created; expert artists would create large, detailed paintings on panes of glass placed between the camera and the set. The result would be that live action fused (hopefully) seamlessly with the matte. The image above is a classic shot from Raiders of the Lost Ark, where you can see the gray region is the clear part of glass through which the scene was shot. As you can imagine, matching the perspective and lighting of the live action is very tricky!
You can find many pictures of classical matte paintings online- for example, see the great list at Shadowlocked. However, I had a hard time finding a good picture showing a glass painting in-line with the camera path to produce a composite. The best I could come up with was this example from a 90’s miniseries called The Last Days of Pompeii, in which the volcano is painted on glass at the upper left and you can see how the painting and real scene line up:
I found this example on the blog Matte Shot, which is a great, detailed resource. This picture is from a long article about master matte artist Leigh Took. In my research, I also enjoyed Raymond Fielding’s book Techniques of Special Effects of Cinematography, which has lots of details on the “good old days”.