After breaking the news about the Book 12 cover earlier this year, I can exclusively confirm that the following will not be the cover for Book 13. But it should be.
There are subtle clues you can pick up that reveal this is not a genuine Wheel of Time cover, most notably that the art is way, way too good to be convincing (it's actually the work of 'Claireduckey' from the Dragonmount forum).
In related news, the prologue to The Gathering Storm has gone on sale, if you have more money than sense ($3 for what should be a free sample? Again?), and Brandon Sanderson should be announcing the newly-decided-on title for Book 13 in the near future.