There's long history between Korean and Japan. The part which is written as Sea of Japan is actually "East Sea" or "Dokdo"
Two countries are very close, and the sea is bit hard to tell which owns this part. However, in so many history background , people are all around the world knew this place as "East Sea" or "Dokdo", even Japaneses knew like that.
However, suddenly some conservative Japanese suggested that this sea is theirs, and saying East sea is Sea of Japan with non-reasonable back-ups. This territory is Korea's.
Also, International Hydrogrphic Organization(IHO) decides to use "East Sea" for this area. It means "East Sea" is the international standard name.
You probably are confused because people can insist something with their own historic background.
However, you should understand with IHQ decision, I hope you should follow the international standards when you upload any article, photos, etc.