Photoshop CS5 enjoys a new paint engine wired up to the new Mixer Brush tool (nested with the Brush tool [B]). To enjoy the benefits, select the new Painting Workspace (Window>Workspace>Painting) and the Mixer Brush tool. Open a conventional photo and have fun experimenting. With more control of brush and fluid dynamics and the ability to mix pixels and to change load, flow, etc., you'll soon be converting photos to paintings. Here I've preserved the photo of my son Miles, while painting over the fall leaves around him.
Adobe Photoshop CS5
By Bryan O'Neil Hughes