The subject of ‘canon’ comes up a lot in Doctor Who circles. Which stories ‘count’? Are the books ‘part of Doctor Who’? and so on.
Rather than address that directly, let’s look at Star Wars, a fictional world which does have an ultimate authority on what’s canon: its creator George Lucas (peace be upon him). Lucasfilm employs people who – presumably amongst other duties – log comments he makes in interviews and incorporates them into the Star Wars canon. If George Lucas says it, it happened. In 2010, Lucas was interviewed by Jon Stewart, who jokingly asked him the nerdy question ‘which planet does Obi Wan Kenobi come from?’. The question is, or rather was, the matter of some debate among Star Wars scholars. Lucas laughed and told Jon Stewart that Obi Wan came from ‘Stewjon’. And thus it was written, and incorporated into canon:
One question that Lucas has never allowed to be discussed is the origins of Yoda. He’s ordered even the slightest statement on the subject excised from the spin off books and comics, he banned a baseball card showing a scene from Yoda’s home planet.
He has apparently joked that Yoda was the illegitimate child of Kermit and Miss Piggy, whisked back through time to avoid a terrible scandal. Using the ‘Stewjon’ rule, that jokes ‘count’, this is therefore the only official origin of Yoda. Which – rather pleasingly, I think – makes this (a genuine photo taken on set) a legitimate, canonical, real, family reunion photo: