This is how to add images to the radmap map with a bit more control over the image than is available by simply adding a bitmap using the pinpoint method.
// Set provider
BingMapProvider provider = new BingMapProvider(MapMode.Aerial, true, "YOUR CODE GOES HERE");
provider.IsTileCachingEnabled = true;
mWindow.radmap.Provider = provider;
// Create information layer
iLayer = new InformationLayer();
iLayer.MapControl = mWindow.radmap;
mWindow.radmap.Items.Add(iLayer);
// Create a new image object and add it to bing map.
Uri uri = new Uri(@"" + imageName, UriKind.Relative);
BitmapImage bitmap = new BitmapImage();
bitmap.BeginInit();
bitmap.UriSource = uri;
bitmap.EndInit();
Image image = new Image();
image.Source = bitmap;
image.Opacity = 0.85;
image.Width = imageWidth;
image.Height = imageHeight;
image.Stretch = Stretch.UniformToFill;
image.SnapsToDevicePixels = true;
image.Name = Name;
// When added to map, centre image over Lat/Long rather than use upper left corner for placement
image.VerticalAlignment = VerticalAlignment.Center;
image.HorizontalAlignment = HorizontalAlignment.Center;
// Add the image to the map
MapLayer.SetLocation(image, new Location(dLatitude, dLongitude));
iLayer.Items.Add(image);