public class FrozenImage : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        ImageSource image = value as ImageSource;
        if (image != null)
        {
            if (image.Dispatcher != null)
            {
                if (image.Dispatcher.CheckAccess())
                {
                    ImageSource returnImage = new BitmapImage();

                    returnImage = image;
                    returnImage.Freeze();

                    return returnImage;
                } else return image.Dispatcher.Invoke(() => Convert(value, targetType, parameter, culture));
            } else return image;
        } else return null;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotSupportedException();
    }
}