private static void WriteMetaDataFile(Photo photo, string targetFileName, Preferences preferences)
 {
     Dictionary<string, string> metadata = preferences.Metadata.ToDictionary(metadatum => metadatum,
         metadatum =>
             photo.GetType()
                 .GetProperty(metadatum)
                 .GetValue(photo, null)
                 .ToString());
     if (metadata.Count > 0)
         File.WriteAllText(string.Format("{0}.json", targetFileName), metadata.ToJson(), Encoding.Unicode);
 }