var directoryname = Path.Combine(Android.OS.Environment.ExternalStorageDirectory.AbsolutePath, "MY_APP");

Directory.CreateDirectory(directoryname);

string jpgFilename = Path.Combine(directoryname, picName);

File.Copy(file.Path, jpgFilename, true);

​

ExifInterface newExif = new ExifInterface(jpgFilename);

newExif.SetAttribute(ExifInterface.TagUserComment, "Ketama126");

newExif.SaveAttributes();