There is a binary that must be downloaded to the cmucam3 camera. The source, etc, for this is in the directory png-robin/. There is also a precompiled hex file that you can use if you don't want to compile the cmucam3-resident application yourself. But you'll still have to download the hex file to the cmucam3 with lpc21isp.
If you want to make changes or recompile the cmucam3-resident application, you should have a working installation of the cmucam3 development environment, and be able to compile the examples in the cc3/projects directory and download the applications to the cmucam3. Once you can do this, you can make a new directory in the projects/ directory of your cmucam3 distribution called png-robin/ and copy the contents of the png-robin/ directory provided with this ROS node into that one. The makefile should then work and provide the correct paths and compile the application.
The cmucam_png node acquires a PNG file from the cmucam3 about once every twenty seconds and publishes it as a compressed image. Acquisition takes around 20 seconds per image because they come over a 115,200 bps serial line. Each PNG image is 352x287 pixels in size. The topic used is named cmucam.
The node is started as follows:
rosrun cmucam_png cmucam_png_server.py