There are several main parts to CpmFetch. Depending on what you want to accomplish, some parts work better than others.
CpmFetch - The main program, allows you to embed tables of images and text into your PHP enabled web pages. They must have access to the CPG database, but otherwise can exist in subdomains (some assembly required for that part). Many options, features and do-hickeys. This is the way you want to go if possible. It can also easily be extended to be used on HTML pages via server side include calls.
CfImageGet - This allows you to grab images via <img src=""> tags from other web sites, html e-mails, or for use as avatars on different forum systems. You call it and it returns the contents of an image file.
CfRSSGet - This provides a customizable way to create RSS feeds for different kinds of information - last updated, most viewed, random, etc...
Coppermine_dao.php The internal workings are exposed as a object, so you can extend the features into new and exciting ways. There is no forum for this, but if you are a developer, the code is pretty easy to understand.