[Zope] How to add new properties to default image objects?

I'd like that all the image objects of my site have more information default fields such as "summary", "keywords", "author", "links", etc, more like an album, and I'm looking forward to modify the Image.py file and its related dtmls. Can anyone explain me what kind of modifications are needed? I know there are photoalbum products out there, but guess I'm just needing the default properties to increase in a few fields. (The fact is that from time to time I need to import a large number of images, and I use ftp for the task. If the default image object already had the mentioned fields, it would be an easier task to just add content to it.) Thanks in advance, Ausum