[Zope] Image Referers

How do I go about writing an access rule for images & binary data (like zip files, mp3's, wavs, etc.) that will return an access denied message if the HTTP_REFERER header doesn't match value(s) that I define? We're trying to discourage direct-linking to our images on other people's sites, but also need to have the ability to have exceptions, i.e. The image is hosted on somesite.com. Anypage from www.somesite.com, www.anysite.com (which is an affiliate), xyz.somesite.com, etc. can also link to the image. If the image isn't called from those pages, return either an access denied message, or an "Image hosted by somesite.com" image.