LoadBitmapFromStream.cs

public void LoadBitmapFromStream()
{
  System.Drawing.Image bmp = System.Drawing.Bitmap.FromFile(@"C:\Temp\test.png");
  MemoryStream strm = new MemoryStream();
  bmp.Save(strm, System.Drawing.Imaging.ImageFormat.Bmp);

  strm.Position = 0;
  System.Drawing.Image img = System.Drawing.Image.FromStream(strm);
  BitmapImage bi = new BitmapImage();
  bi.BeginInit();
  MemoryStream ms = new MemoryStream();
  img.Save(ms, System.Drawing.Imaging.ImageFormat.Bmp);

  ms.Seek(0, SeekOrigin.Begin);
  bi.StreamSource = ms;
  bi.EndInit();
  imgBox.Source = bi;
}