'Modifies the images of a clip by replacing the frame
`get_frame(t)` by another frame,  `image_func(get_frame(t))`'

def fl_image(self, image_func, apply_to=None):

    if (apply_to is None):
        apply_to = []
    return self.fl((lambda gf, t: image_func(gf(t))), apply_to)
