trouble with forcing output to be cached

Hallo all, I would like to force PHP generated images to cache on client-side. just for reduce traffic and speed of pageloading. The problem is that PHP adds some headers by default, They are: Cache-Control : no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma : no-cache :) it is possible to rewite Cache-Control header with "private" ar "public" values. bet Pragma do not have positive value :) so i found that i cant set Empty header("Pragma: "); :) and it works :) except one browser - Opera :). i know that it is Operas problem, but is there any idea to absolutely remove response header ? or block PHP to add its own headers ? -- Ilja Polivanovas