Content enumeration

Hello everyone, I'm working on a widget that could display the complete structure of Pier (actually based on something like PRTreeWidget). The widget is here for displaying purpose and it instanciates a visitor which walk over the structure and gather the information. I assume that I need this visitor if I want to achieve my goal but a question remains: what if I want to list every piece of content like images,...? For example, I have a page with an image and my widget shows: a PRDocument PRInternalLink PRText How can I know if there is an image here? In other words how could I display more details? Cheers, Sébastien