If you are looking to blit the bitmap directly to the window, and you wish to directly control the rendering you may simply override the OnRender function. However there is on catch (noted in the comments of the code)...
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.Background = Brushes.Transparent; // <-- necessary (strange bug)
// Charles Petzold writes about this at the following link:
// http://social.msdn.microsoft.com/Forums/vstudio/en-US/750e91c2-c370-4f0a-b18e-892afd99bd9b/drawing-in-onrender-beginnerquestion?forum=wpf
}
protected override void OnRender(DrawingContext drawingContext)
{
base.OnRender(drawingContext);
BitmapSource bitmapSource = new BitmapImage(new Uri("C:\\Temp.png", UriKind.Absolute));
CroppedBitmap croppedBitmap = new CroppedBitmap(bitmapSource, new Int32Rect(20, 20, 100, 100));
drawingContext.DrawImage(croppedBitmap, new Rect(0.0d, 0.0d, this.RenderSize.Width / 2.0d, this.RenderSize.Height));
}
}