Hi!
My sister tell me she forgot to take a picture of the ocean and now futher in the game she's block and it's no more possible to take a picture on the ocean. Is it possible?

Thanks!

Yes, most of the pictures must be taken at a specific point in the game.
But you can always use an old savegame to unlock pictures you missed since they are unlocked for the extras-menu and not for one specific savegame.

Ok thank, my sisters restart the game.

But pictures are not essential to complete the game?

No, they are not.
As far as I remember you only need them to unlock stuff in the extras-section, like e.g. pictures and movies from the game.