[Zope] Browser Sticky Fingers

[Jeff Rush]

I'm pulling my hair out here over what is probably a simple HTTP issue.
I have a Zope method that stuffs a new image into a Zope Image object,
based on the content of the page where the method is called.

The problem is that the image is not updated until I exit the browser,
and then flush all of it's caches manually.

I've turned off any proxy support, configured Netscape 4.x with the
option "Document in cache is compared to document on web site [always]",
and even run the 'curl' utility outside of the browser that prints the
HTTP headers.  The headers show that the modified date is changing,
the size is changing (different image sizes), and that there is no expire
header.  I thought maybe I needed one but noticed that no where in
the Zope source code do they use one, and when one of their
images is re-uploaded via the /manage_upload, it displays correctly.

Am I missing something simple?

-Jeff Rush