Hi,
After do some test, i found FileObserver works ok, i had a confusion:
Camera was configured to save photos at SD folder /DCIM/Camera
FileObserver was configured to watch file.DirExternalRoot & "/DCIM/Camera"
Both folders exists but are not the same folder.
After verify that file.DirExternalRoot & "/DCIM/Camera" is not the same path than SD folder /DCIM/Camera,
i configure camera to save photos into file.DirExternalRoot & "/DCIM/Camera"
Now FileObserver fire events when i take photo with camera native app and works ok.
So now i can configure app to react immediately or send at x minutes interval.