Вот кусочек от developers.google.com/speed/pagespeed
http://www.woodfun.ru/images/bb.gif (expiration not specified)
http://www.woodfun.ru/images/bulletL1.jpg (expiration not specified)
<IfModule mod_headers.c>
ExpiresActive On
ExpiresByType image/jpg "access 1 week"
ExpiresByType image/jpeg "access 1 week"
ExpiresByType image/gif "access 1 week"
ExpiresByType image/png "access 1 week"
ExpiresByType text/x-javascript "access 1 week"
ExpiresDefault "access 1 week"
</IfModule>
<IfModule mod_expires.c>
ExpiresActive on
ExpiresDefault "access plus 1 month"
ExpiresByType text/cache-manifest "access plus 0 seconds"
<FilesMatch \.(html|xhtml|xml|shtml|phtml|php|txt)$>
ExpiresDefault "access plus 0 seconds"
</FilesMatch>
ExpiresByType text/html "access plus 0 seconds"
ExpiresByType text/xml "access plus 0 seconds"
ExpiresByType application/xml "access plus 0 seconds"
ExpiresByType application/json "access plus 0 seconds"
ExpiresByType application/rss+xml "access plus 1 hour"
ExpiresByType application/atom+xml "access plus 1 hour"
<FilesMatch \.(ico)$>
ExpiresDefault "access plus 1 week"
</FilesMatch>
ExpiresByType image/x-icon "access plus 1 week"
<FilesMatch \.(gif|png|jpg|jpeg|ogg|mp4|mkv|flv|swf|wmv|asf|asx|wma|wax|wmx|wm)$>
ExpiresDefault "access plus 1 year"
</FilesMatch>
ExpiresByType image/gif "access plus 1 month"
ExpiresByType image/png "access plus 1 month"
ExpiresByType image/jpeg "access plus 1 month"
ExpiresByType video/ogg "access plus 1 month"
ExpiresByType audio/ogg "access plus 1 month"
ExpiresByType video/mp4 "access plus 1 month"
ExpiresByType video/webm "access plus 1 month"
ExpiresByType text/x-component "access plus 1 month"
<FilesMatch \.(eot|ttf|otf|svg|woff)$>
ExpiresDefault "access plus 1 year"
</FilesMatch>
ExpiresByType application/x-font-ttf "access plus 1 month"
ExpiresByType font/opentype "access plus 1 month"
ExpiresByType application/x-font-woff "access plus 1 month"
ExpiresByType image/svg+xml "access plus 1 month"
<FilesMatch \.(css|js)$>
ExpiresDefault "access plus 1 year"
</FilesMatch>
ExpiresByType text/css "access plus 1 year"
ExpiresByType application/javascript "access plus 1 year"
</IfModule>