mod_deflate is gzipping my png images -- is there anyway t..

Hi,
I'm trying to get mod_deflate to not compress my images based on the
mime-type (image/png) in the document not the request uri. I currently
have a bunch of servlets that output pngs, but lack a file extension
of .png. So the common idiom of using the following line:

SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-gzip dont-vary

doesn't work for me because my images are at urls like http://abcwebsite.com/photo
and http://abcwebsite.com/makephoto. Is there anyway to match the mime-
type of the content instead of the extension? I was attempting to set
an environment variable in my modpython servlets but I couldn't seem
to get apache to see it.

Version info: Apache/2.0.59 (Unix) mod_ssl/2.0.59 OpenSSL/0.9.7b DAV/2
mod_python/3.1.4 Python/2.4

Thank you all,
Mike