photos.pick_image() must be called before scene.Scene.setup(). However...<br />scene.load_pil_image() must be called in or after scene.Scene.setup().
From Brumm's excellent photo_text.py example, try the syntax:
self.img = photos.pick_image()
self.img = scene.load_pil_image(self.img)
See his example for dealing with self.img in your setup() and other scene.Scene methods().