How to save captured images into media store?

I want to store captured images from the camera on a way, that they where shown in the gallery.

If I use the fs.writeFile like in the snippet fs.jsx it will store it into fs.cacheDir.
I know I can change this into fs.filesDir, but I don't find the file.
it stores it into:
/data/user/0/com.eclipsesource.tabris.js/files/media/test.jpg

Do I have to change the directory name into something special?
It should work on ios as well.