<Image x:Name="MyImage" Source="Assets/luigi.jpg" HorizontalAlignment="Left" Height="100" Margin="285,400,0,0" VerticalAlignment="Top" Width="100" RenderTransformOrigin="0.587,0.507"/>

private void ImageCheckBox_Tapped(object sender, TappedRoutedEventArgs e)
        {
            MyImage.Source = I CAN'T FIGURE OUT WHAT TO DO HERE;
        }