Optimizasyon işlerinde .htaccess dosyası da etkilidir.
Benim kendi kullandığım .htaccess dosyasının kodlarını sizlerle paylaşıyorum. Çoğu imajların önbelleklemesini bu kodlarla sağlayabilirsiniz.

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

<ifModule mod_gzip.c>
mod_gzip_on Yes
mod_gzip_dechunk Yes
mod_gzip_item_include file .(html?|txt|css|js|php|pl)$
mod_gzip_item_include handler ^cgi-script$
mod_gzip_item_include mime ^text/.*
mod_gzip_item_include mime ^application/x-javascript.*
mod_gzip_item_exclude mime ^image/.*
mod_gzip_item_exclude rspheader ^Content-Encoding:.*gzip.*
</ifModule>

<IfModule deflate_module>
	<IfModule filter_module>
		AddOutputFilterByType DEFLATE text/plain text/html
		AddOutputFilterByType DEFLATE text/xml application/xml application/xhtml+xml application/xml-dtd
		AddOutputFilterByType DEFLATE application/rdf+xml application/rss+xml application/atom+xml image/svg+xml
		AddOutputFilterByType DEFLATE text/css text/javascript application/javascript application/x-javascript
	</IfModule>
</IfModule>


# Enable GZIP 
<ifmodule mod_deflate.c> 
AddOutputFilterByType DEFLATE text/text text/html text/plain text/xml text/css application/x-javascript application/javascript 
BrowserMatch ^Mozilla/4 gzip-only-text/html 
BrowserMatch ^Mozilla/4\.0[678] no-gzip 
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html 
</ifmodule> 

# Expires Headers - 2678400s = 31 days 
<ifmodule mod_expires.c> 
	ExpiresActive On 
	ExpiresDefault A0
	ExpiresByType image/gif "access 1 year"
	ExpiresByType image/png "access 1 year"
	ExpiresByType image/jpeg "access 1 year"
	ExpiresByType image/jpg "access 1 year"
	ExpiresByType image/ico "access 1 year"
	ExpiresByType image/svg+xml "access 1 month"
	ExpiresByType text/css "access 1 month"
	ExpiresByType text/javascript "access 1 month"
	ExpiresByType application/javascript "access 1 month"
	ExpiresByType application/x-javascript "access 1 month"
</ifmodule> 
  
# Cache Headers 
<ifmodule mod_headers.c> 
  # Cache specified files for 31 days 
  <filesmatch "\.(ico|flv|jpg|jpeg|png|gif|css|swf)$"> 
  Header set Cache-Control "max-age=2678400, public" 
  </filesmatch> 
  # Cache HTML files for a couple hours 
  <filesmatch "\.(html|htm)$"> 
  Header set Cache-Control "max-age=7200, private, must-revalidate" 
  </filesmatch> 
  # Cache PDFs for a day 
  <filesmatch "\.(pdf)$"> 
  Header set Cache-Control "max-age=86400, public" 
  </filesmatch> 
  # Cache Javascripts for 31 days 
  <filesmatch "\.(js)$"> 
  Header set Cache-Control "max-age=2678400, private" 
  </filesmatch> 
</ifmodule>  

# ----------------------------------------------------------------------
# Webfont access
# ----------------------------------------------------------------------

# allow access from all domains for webfonts
# alternatively you could only whitelist
#   your subdomains like "sub.domain.com"

<FilesMatch "\.(ttf|otf|eot|woff|font.css)$">
  <IfModule mod_headers.c>
    Header set Access-Control-Allow-Origin "*"
  </IfModule>
</FilesMatch>

# webfont mime types
AddType application/vnd.ms-fontobject  eot
AddType font/truetype                  ttf
AddType font/opentype                  otf
AddType application/x-font-woff              woff

# webfonts and svg:
<IfModule mod_deflate.c>
  <FilesMatch "\.(ttf|otf|eot|svg)$" >
    SetOutputFilter DEFLATE
  </FilesMatch>
</IfModule>
<IfModule mod_headers.c>
Header set Connection keep-alive
Header set Expires "max-age=2592000, public"
Header unset ETag
</IfModule>
# END WordPress