How to publish batch of images in a python node with ROS 2?

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I have a publisher in ROS 2 which publishes an image message as following:

import rclpy
from rclpy.node import Node
from std_msgs.msg import String
from cv_bridge import CvBridge
from sensor_msgs.msg import Image
import cv2
import numpy as np

class MinimalPublisher(Node):
      def __init__(self):
         super().__init__('minimal_publisher')
         self.publisher_ = self.create_publisher(Image, 'Image', 10)
         timer_period = 0.5  # seconds
         self.timer = self.create_timer(timer_period, self.timer_callback)
         self.i = 0
         self.im_list = []
         self.cv_image = cv2.imread('test.jpg') ### an RGB image 
         self.bridge = CvBridge()

      def timer_callback(self):
         self.publisher_.publish(self.bridge.cv2_to_imgmsg(np.array(self.cv_image), "bgr8"))
         self.get_logger().info('Publishing an image')

def main(args=None):
    rclpy.init(args=args)
    minimal_publisher = MinimalPublisher()
    rclpy.spin(minimal_publisher)
    minimal_publisher.destroy_node()
    rclpy.shutdown()

if __name__ == '__main__':
   main()

It works fine with a single image. But I want to publish a batch of images with the given shape:

[12, 3, 224, 224] => [batch, channel, width, height]

I tried to send it as a list of images but it failed. Also, I wanted to build a custom message as following but it doesn't work too:

uint32 height 224
uint32 width 224
string encoding "bgr8"
uint8[150528] data

More info:

python 3.6
ROS 2 - eloquent (build from source)
Ubuntu 18

How should I pass a batch of images to the subscriber?