How to add multiple publishers to get 4 camera images?

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Hai, I am writing a rospy code to publish images from 4 cameras. Currently, i trying it with my laptop camera.it works..but how to add multiple publishers for camera. My code is...

#!/usr/bin/env python

import rospy
from sensor_msgs.msg import Image
import cv2
import numpy as np
from cv_bridge import CvBridge, CvBridgeError

def webcam_pub():
    pub = rospy.Publisher('webcam/image_raw', Image, queue_size=1)
    rospy.init_node('webcam_pub', anonymous=True)
    rate = rospy.Rate(60) # 60hz

    cam = cv2.VideoCapture(0)
    bridge = CvBridge()

    if not cam.isOpened():
         sys.stdout.write("Webcam is not available")
         return -1

    while not rospy.is_shutdown():
        ret, frame = cam.read()

        cv2.imshow("camera1",frame)
        cv2.waitKey(1)
        msg = bridge.cv2_to_imgmsg(frame, encoding="bgr8")
        if ret:
             rospy.loginfo("Capturing image failed.")

        pub.publish(msg)
        rate.sleep()


if __name__ == '__main__':
    try:
        webcam_pub()
    except rospy.ROSInterruptException:
      pass

I am using UBUNTU 16.04, KINETIC distro.