I know this is quite a few months late, but I caught something weird on the third episode of Fringe this year. While Peter has been erased from reality, Walter and Olivia have been dreaming/hallucinating about him. Olivia's even sketched him, to prove they're talking about the same person:
No, writers, the problem isn't that there's no one who looks like Joshua Jackson in the whole world (which is a strange enough concept), but that the sketch only looks basically like him. There have to be literally thousands of people who have those same facial features, so the problem with using facial recognition would be a flood of results so large that it would be impossible for them to cope with.
Also causing problems? The fact that later in the season, when Walter has convinced himself that Peter is unconsciously using psychic powers to make Olivia remember his universe, both of them seem to have conveniently forgotten that they each remembered him before he 'jumped' into their world.