Flutter How to save File? image to gallery by using path in android

Question

File? imager = _EncryptState.image;//this image come from gallery by image_picker
_encodeimage() async {
    final File? file = await Steganograph.encode(
        image: imager!,
        message: 'message',
        encryptionKey: 'keyen',
        outputFilePath: 'storage/emulated/0/Pictures/output.png');
  }

normally outputFilePath from steganograph.dart use save on this (https://i.stack.imgur.com/DNlkr.png)

File? imager = _EncryptState.image;//this image come from gallery by image_picker
_encodeimage() async {
    final File? file = await Steganograph.encode(
        image: imager!,
        message: 'message',
        encryptionKey: 'keyen',
        outputFilePath: 'storage/emulated/0/Pictures/output.png');
  }

i use package:steganograph/steganograph.dart and for outputFilePath i want to save it on my android emulator