The Output class is the parent class for all the Output modules
in the system, and so it is conceptually abstract -- it defines its destructor
and the putImage() methods as virtual.18 However, it provides a minimal null implementation of an Output module,
which always returns true from putImage(), and hence requests the system
exits after the first image, which is discarded.
Valid names for this module are null, none and void, and it takes no parameters.