I have a website whose maintenance I've inherited, which is a big hairy mess.
One of the things i'm doing is improving performance. Among other things, I'm adding Expires headers to images.

Now, there are some images that are served through a PHP file, and I notice that they do have the Expires header, but they also get loaded every time.

Looking at Response Headers, I see this:

Expires Wed, 15 Jun 2011 18:11:55 GMT
Cache-Control   no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma  no-cache

Which obviously explains the problem.

Now, i've looked all over the code base, and it doesn't say "pragma" anywhere. .htaccess doesn't seem to have anything related either.

Any ideas who could be setting those "pragma" (and "cache-control") headers, and how I can avoid it?

Thanks!
Daniel