|OK, I saw (and enjoyed) it again and I'm sticking by my interpretation. The scene you mentioned is one of the last shots in the movie, flashing briefly while Leonard is giving his soliloquy about what keeps him going in spite of it all. The woman in the shot is his wife, but she's just a dream, or fiction, of his tattoo-covered "present self"--a much-revisited image that keeps him going, like the polaroids or the notes he consults. The movie intends no "Verbal-Kint-is-Keyser-Soze" twist as in The Usual Suspects (thank god)--a last minute revelation that supposedly makes you rethink the whole movie. Memento is a better film because there's a plot reason for all the red herrings. (It did look like Leonard's tattoos were slightly different in that shot, however; more likely it's a continuity error rather than some ominous clue.)
I think that the film is intentionally filled with enough contradictions and inconsistancies to make it work in multiple "whodunnit" configurations.