How to Save sensor_msgs/Image

edit

I've got Gazebo 2.2.3 and ROS Indigo set up, and I have a plugin that allows a stereo camera to publish images from Gazebo to ROS. I've run rosbag with the image topics, and it has no problems recording or playing them. The issue now is that I need to somehow either save the images themselves or have access to the pointers for the camera images. Can someone give me some pointers on how to do so, preferably via C++ code?