Inspired by another question I am curious. Say a druid has never seen a bear (as an example; any particular beast will do), but has seen an illusion of a bear, and furthermore failed their save vs. the illusion (so they believe they saw a bear). Could they wild shape into a bear?
Unfun answer: Strict RAW - No
Starting at 2nd level, you can use your action to magically assume the shape of a beast that you have seen before.
A strict RAW reading of this would say no for the simple fact that seeing an illusion of something is not actually seeing the creature in the plain English sense of the word.
Jeremy Crawford said something that works well as a rationalization for this requirement too:
It's easy to rationalize that part of the magic relies on you seeing the real creature like somehow its essence... you're drawing on it in some way when you cast the spell. (Dragon Talk - 10/26/17 52:45)
He is actually talking about Shapechange when he says that but Shapechange has the exact same wording for this as Wild Shape so it should be applicable.
However, it is easy to see that this can easily devolve into, well what DOES qualify as seeing the creature then? Crystal ball? Telescope? What counts and what doesn't?
Better answer: DM Fiat
The RAW ruling seems overly strict for me as well as prone to misinterpretation and argument. There are just some places where the rules do not have a clear answer. This is why we have a DM to fill in the gaps.
I think having the DM rule on this on a case-by-case basis will make for a more fun, more empowering result. Especially since the Wild Shape list is so limited that it is not really prone to abuse.
And I'm not the only one who thinks that: In that same interview Crawford is asked:
Would you ever rule that if did it from an illustration or an imperfect way not having seen it themselves they would get it wrong? (ibid)
To which he responds that he would often rule in cases like this that
It does work, but the results are not what you expect...[making sure the effects are] still effective or amusing. [This] is entirely in the realms of DM adjudication because the spell itself say you've got to see it. (ibid)
For DMs, instead of saying no to this request, why not make it interesting? Since they are not technically meeting the requirements for the ability, have the animal look a bit weird or have abilities that are slightly off.
Depending on the nature of the illusion, how long the player saw it for, how well they saw it, etc the DM could have many creative responses to attempting this. It could lead to some fun and interesting stories, which is what this game is all about right?