Leverage browser caching issue
Read this article about Leverage Browser Caching for Images, CSS and JS.

Add these lines to your .htacess file.

## EXPIRES CACHING ##
&lt;IfModule mod_expires.c&gt;
ExpiresActive On
ExpiresByType image/jpg "access 1 year"
ExpiresByType image/jpeg "access 1 year"
ExpiresByType image/gif "access 1 year"
ExpiresByType image/png "access 1 year"
ExpiresByType text/css "access 1 month"
ExpiresByType application/pdf "access 1 month"
ExpiresByType application/javascript "access 1 month"
ExpiresByType application/x-javascript "access 1 month"
ExpiresByType application/x-shockwave-flash "access 1 month"
ExpiresByType image/x-icon "access 1 year"
ExpiresDefault "access 2 days"
&lt;/IfModule&gt;
## EXPIRES CACHING ##


Also you can try 

&lt;FilesMatch "\.(jpg|jpeg|png|gif|swf)$"&gt; Header set Cache-Control "max-age=604800, public" &lt;/FilesMatch&gt;