draw the thumbnail on the image

def draw(self, img, pixmapper, bounds):
        '''draw the thumbnail on the image'''
        if self.hidden:
            return
        thumb = self.img()
        (px,py) = pixmapper(self.latlon)

        # find top left
        (w, h) = image_shape(thumb)
        px -= w//2
        py -= h//2

        (px, py, sx, sy, w, h) = self.clip(px, py, w, h, img)

        thumb_roi = thumb[sy:sy+h, sx:sx+w]
        img[py:py+h, px:px+w] = thumb_roi

        # remember where we placed it for clicked()
        self.posx = px+w//2
        self.posy = py+h//2