[Zope] Serverside Browser detection

[Robin Becker]

I would like to detect whether the client browser can render png images. I see the
following from Netscape 4.61
HTTP_ACCEPT     image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, image/png, */*
HTTP_USER_AGENT Mozilla/4.61 [en] (Win95; I)

and this from MSIE 5.0
HTTP_ACCEPT     image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, 
                application/vnd.ms-excel, application/msword, */*
HTTP_USER_AGENT Mozilla/4.0 (compatible; MSIE 5.0; Windows 95; DigExt;
                        btclick.com Build BTCFUNFD1)

I know that MSIE 5.0 can render png's (by observation) and by report that Netscape 3.x
cannot.

Question:
Parse HTTP_USER_AGENT to determine netscape/msie or do I rely on the apparently unreliable
HTTP_ACCEPT?
-- 
Robin Becker