<Grid x:Class="XXX.View.ScreenPartPicture"
DataContext="{Binding PictureViewModel, Source={StaticResource Locator}}">
        <Image Source="{Binding Image, IsAsync=True}" />
    </Grid>

public class PictureViewModel : ViewModelBase
{
    private BitmapImage _image;

    public BitmapImage Image
    {
        get { return _image; }
        set { Set(ref _image, value); }
    }

    public void CleanUp()
    {
        Image = null;
    }
}