How to apply a drop shadow effect when drawing to a DrawingContext in WPF?
See the question and my original answer on StackOverflowIf you're running on .NET Framework 3.5 SP1 or higher, you should use UIElement.Effect or Visual.VisualEffect (this one is protected so you would need to derive from it) instead, with an instance of System.Windows.Media.Effects.DropShadowEffect.