This cover for The Winds of Winter has been around for a long time, but there’s been persistent uncertainty over whether it’s the official cover for the book or it’s a well-made piece of fan-art. The full cover, if you haven’t seen it:
It certainly looks like a Song of Ice and Fire cover, which is to say that it features a single object in the foreground (a sword in A Game of Thrones, a crown in A Clash of Kings, etc.), and a simple background. Now, George R.R. Martin has confirmed that this is indeed the official cover, at least for the moment. He revealed it when responding to a comment on his Not a Blog.
"playstationsupe: George is the black cover with the horn the real cover or not?grrm: Yes, for the moment.Though these things have been known to change."
So there you go. It’s real. Another pertinent question: what is that horn? The most likely candidates are the Horn of Joramun, a legendary horn said to be able to bring down the Wall, and Dragonbinder, an object Euron Greyjoy brought back from the ruins of Valyria. Supposedly, it has the power to control dragons.
It seems more likely that this is Dragonbinder, as it matchers the description in A Feast for Crows (shiny, with strange glyphs). Also, Melisandre burned what Mance Rayder claimed was the Horn of Joramun in A Dance with Dragons, so unless it turns up elsewhere, it’s not likely to play a part in The Winds of Winter.
Dragonbinder, on the other hand, is on its way to Meereen in the hands of Victarion Greyjoy, who plans to use it take control of Daenerys’ dragons. If it’s on the cover, we can expect it to play a big role.
One other possibility: George R.R. Martin published The Winds of Winter in 1980 under a pseudonym, and we’ve known about the cover for years: