There's a constant doubling and redoubling of every sign. Midge paints herself in place of Madeleine as Carlotta, based in turn on a painting. But Scotty rejects Midge's portrait. It's not about resemblances. It's about indexes.
Signs have causes, but they are different to their causes, and cause in turn more differences.
A great deal of the film has Scotty simply looking out of the windscreen of his car, following Madeleine. He is of course the cinema viewer, seated in the cinema, watching moving pictures. The reverse shot shows what he sees, and the windscreen seems about the same aspect ratio as widescreen cinema. But this isn't just a film about film and watching film. It's a film about death, and the vectors through which death is remembered and experienced remotely.