To enable image caching within apache you must have the mod_headers module and the mod_expires module installed.

See http://httpd.apache.org/ for more information on installing.

To enable image caching you must edit either the apache configuration file (httpd.conf) or the web sites ".htaccess" file.

Add in the following to the file

<FilesMatch "\.(jpg|jpeg|png|gif)$">

Header set Cache-Control "max-age=604800, public"

</FilesMatch>

*Note: 604800 is equal to 7 days. You may higher or lower this value.