PrintDialog pd = new PrintDialog();
                  
            Image image = new Image();
            image.Source=new BitmapImage(new Uri(mainImage.Source.ToString()));
            pd.PrintVisual(image, "");

 PrintDialog pd = new PrintDialog();
            // Just load image       
            BitmapImage bi = new BitmapImage();
            bi.BeginInit();;
            bi.UriSource=new Uri(mainImage.Source.ToString());
            bi.DecodePixelWidth = 400;
            bi.EndInit();

            // and draw it in virtual source
            DrawingVisual vi = new DrawingVisual();
            DrawingContext dc = vi.RenderOpen();
            dc.DrawImage(bi, new Rect { Width = bi.Width, Height = bi.Height });
            dc.Close();
            pd.PrintVisual(vi, "");