How to swap images based on the current theme WP7

 Height="30" HorizontalAlignment="Center" Margin="0,0,0,220" Name="imgDark" Stretch="Fill" Visibility="{StaticResource PhoneLightThemeVisibility}" VerticalAlignment="Center" Width="30" Source="/MyApplication;component/imageDarkTheme.png" />
 Height="30" HorizontalAlignment="Center" Margin="0,0,0,220" Name="imgLoading" Stretch="Fill" Visibility="{StaticResource PhoneDarkThemeVisibility}" VerticalAlignment="Center" Width="30" Source="/MyApplication;component/imageLightTheme.png" />