1- create a ros package. Here baxter_srv is the package name

   roscreate-pkg baxter_srv std_msgs rospy roscpp baxter_interface  sensor_msgs
   
   rosmake baxter_srv
   
   adjust your CMakeLists.txt file you have to uncomment rosbuild_genmsg() and rosbuild_gensrv()

2-add srv file:

   sensor_msgs/Image last_image

Right_hand_camera.py is the serive which should be running constantly and it gets the image from baxter' right-hand camera.

To get the last image you should:

   rospy.wait_for_service('last_image')

   self.rightHandCamera = rospy.ServiceProxy('last_image', ImageSrv)

   request = self.rightHandCamera()

   imgmsg = request.last_image

An example to use this service is baxter.py in MIDCA/examples in Baxter branch

Getting help from this link: http://nildo.github.io/organizer-baxter/