The plugin JAR files provided for the different book editions (https://sourceforge.net/projects/imagingbook/files/code/plugins/) are supposed to be downloaded and placed inside the ImageJ/plugins/ folder. If simply placed there, ImageJ should (after a restart) recognize the .jar file as a plugin container and show all plugins in the Plugins menu. However, this only works if the name of the .jar file contains at least one underscore character! All plugin archives were thus renamed tp BurgerBurgeXxx_plugins.jar. Users may either rename local files themselves or download a new copy.
Alternatively (e.g. to edit the plugin code), the plugin .jar archives may be expanded (unzipped) inside the plugins folder. NOTE: Make sure to expand in place (‘here’), i.e., without introducing an additional directory level! The chapter folders must show directly inside the plugins folder:
Mac users should be aware that the built-in Archive Utility always unzips to a new folder with the same name as the archive file. In this case, the contained book chapter folders must be moved up manually by one level (into the ImageJ/plugins/ folder).