Quick example of how to set default expires headers. This will help prevent browsers from re-downloading the same images more than once and therefore reduce the load on your image server.

Put this in your .htaccess file:

<IfModule mod_expires.c>
        ExpiresActive on
        ExpiresByType image/gif "access plus 10 years"
        ExpiresByType image/jpeg "access plus 10 years"
        ExpiresByType image/png "access plus 10 years"
        ExpiresByType text/css "access plus 10 years"
        ExpiresByType text/js "access plus 10 years"
        ExpiresByType text/javascript "access plus 10 years"
        ExpiresByType application/javascript "access plus 10 years"
        ExpiresByType application/x-javascript "access plus 10 years"
        #ExpiresDefault "access plus 1 days"
</IfModule>