It is a flashback >_>........... Check around the picture, it's dark. Flashback..
Check the hair, its identical.
And it has been confirmed that Zeref and Natsu had some connection back then.
I didn't notice the dark edges, however Romeo has the same hair (though Romoe being there doesn't make much sense ), so that isn't really a big argument but they indeed have very similar hair.
There is a reasonable chance it is Zeref, however there are still a lot of loose ends there.
And what has been confirmed was that Zeref knows Natsu, however that's it. So at this point at most it's Zeref who has some kind of connection with Natsu and we have no clue from when that connection was. After all there's something very fishy with both Zeref as the dragon slayer's ages.
He has the FT symbol on his arm, however at the time Natsu joined FT people like Erza and Gray already were member of FT + there should tons of others. None of the people so far that saw him recognized him, including Natsu, while normally he should even know his smell if they ever met before. But above all how can no one know that Zeref is in FT? Or that Zeref is walking on Fairy Island without having a clue.
Unless that person is some kind of Jinchuriki with Zeref as the tailed beast.
