[Zope] Filtering Content

I am looking for a way to filter out <IMG> tags from a Zope site. I'm using Zope 2.5.0 + CMF + CMFWiki. I have managed to modify the render routine of CMFWikiPage, but the request argument is empty, so I can't check to see if a cookie has been set. What I want to do is examine a cookie called TextOnly. If the value is 1, then the filter will replace all the Image tags with the ALT text. Otherwise, the filter will not be called. As the code stands now, it's only modifying the contents of CMFWiki pages, leaving the outer framework of the site intact. What I want is to replace ALL image tags, so I need to get at something higher-level, like the entire HTML text just before it gets sent back to the browser. Jeff