private async void btnThumb_Tapped(object sender, TappedRoutedEventArgs e)
        {
            FileOpenPicker openPicker = new FileOpenPicker();

            openPicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;
            openPicker.ViewMode = PickerViewMode.Thumbnail;

            // Filter to include a sample subset of file types.
            openPicker.FileTypeFilter.Clear();
            openPicker.FileTypeFilter.Add(".bmp");
            openPicker.FileTypeFilter.Add(".png");
            openPicker.FileTypeFilter.Add(".jpeg");
            openPicker.FileTypeFilter.Add(".jpg");

            // Open the file picker.
            StorageFile file = await openPicker.PickSingleFileAsync();

            BookViewModel.LoadFile(file);

            // 'file' is null if user cancels the file picker.
            if (file != null)
            {
                //Open a stream for the selected file.
                //The 'using' block ensures the stream is disposed
                //after the image is loaded.
                using (Stream stream = await file.OpenStreamForReadAsync())
                {
                    byte[] bytes = new byte[stream.Length];
                    await stream.ReadAsync(bytes, 0, bytes.Length);

                    BookViewModel.Image = bytes;
                }
            }
        }