how to set expiration time for images
# BEGIN EXPIRES
<IfModule mod_expires.c>
ExpiresActive On
ExpiresDefault "access plus 10 days"
ExpiresByType text/css "access plus 1 week"
ExpiresByType text/plain "access plus 1 month"
ExpiresByType image/gif "access plus 1 month"
ExpiresByType image/png "access plus 1 month"
ExpiresByType image/jpeg "access plus 1 month"
ExpiresByType application/x-javascript "access plus 1 month"
ExpiresByType application/javascript "access plus 1 week"
ExpiresByType application/x-icon "access plus 1 year"
</IfModule>
# END EXPIRES