set the currently displayed image

def set_image(self, img, bgr=False):
        '''set the currently displayed image'''
        if not self.is_alive():
            return
        if not hasattr(img, 'shape'):
            img = np.asarray(img[:,:])
        if bgr:
            img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
        self.in_queue.put(MPImageData(img))