The mod_expires module can be used for setting only max-age directive but what is you want to configure the proxy related directives say you want to set Cache-Control to something like this
Cache-Control max-age=7776000, public,s-maxage=2592000
This means the browser can cache the resource for 3 months but the public cache, such as cache proxy can cache it for 1 month.
You should use mix of mod_expires and mod_headers to set these headers by adding following lines to the httpd.conf
ExpiresDefault "access plus 3 month"
Header append Cache-Control "public,s-maxage=2592000"
This configuration will tell Apache HTTP Server to set 3 month caching for browser and 1 month caching for cache proxy only for resources with
This is screen shot of Firefox when i try to access a image from HTTP server that has the above configuration