If you do not export the Class Hierarchy (Inheritance Hierarchy section in Visual Studio templates) section in your configuration, class hierarchy images are not shown in this output format. Regardless of this setting images of class hierarchies are generated (if the option above is turned on) and you can insert them in your documentation.

local class hierarchy A graphical representation of the class relationships of the current class in the Class Hierarchy (Inheritance Hierarchy in Visual Studio templates) section. 

modules A Doc-O-Matic feature that lets you divide large projects into smaller parts.