GScreenOverlay
Its very similar to GGroundOverlay, with the difference that using GScreenOverlay the image showed is static (doesn't change it's absolut position when the map is moved).
Code.aspx
<cc1:GMap ID="GMap1" runat="server" />
Code.aspx.cs
GLatLng sw = new GLatLng(64, 20);
GLatLng ne = new GLatLng(65, 29);
GMap1.setCenter((sw / 2) + (ne / 2));
GScreenOverlay screenOverlay = new GScreenOverlay("http://googlemaps.subgurim.net/images/logo.jpg",
new GScreenPoint(0, 21, unitEnum.pixels, unitEnum.pixels),
new GScreenPoint(0, 0),
new GScreenSize(0, 0));
GMap1.Add(screenOverlay);