浏览器不缓存.png图像

Question

我正在使用Google Page Insights来测试我的网页，并建议我启用缓存控制和通缩。所以我打开了所需的模块（mod_cache.so，mod_deflate.so，mod_headers.so，mod_filter.so，mod_expires.so）并修改了我将在下面包含的.htaccess文件。 Google Page Insights仍然无法接受压缩，出于某种原因.png图片不会被缓存。请指教......

RewriteEngine On

<IfModule mod_expires.c>
  ExpiresActive On
  # Perhaps better to whitelist expires rules? Perhaps.
  ExpiresDefault "access plus 1 month"

  # Your document html
  ExpiresByType text/html "access plus 4 hours"

  # Data
  ExpiresByType text/xml "access plus 0 seconds"
  ExpiresByType application/xml "access plus 0 seconds"
  ExpiresByType application/json "access plus 0 seconds"

  # RSS feed
  ExpiresByType application/rss+xml "access plus 1 hour"

  # Favicon
  ExpiresByType image/x-icon "access plus 1 year"

  # Media: images, video, audio
  ExpiresByType image/gif "access plus 2 weeks"
  ExpiresByType image/png "access plus 2 weeks"
  ExpiresByType image/jpg "access plus 2 weeks"
  ExpiresByType image/jpeg "access plus 2 weeks"
  ExpiresByType video/ogg "access plus 2 weeks"
  ExpiresByType audio/ogg "access plus 2 weeks"
  ExpiresByType video/mp4 "access plus 2 weeks"
  ExpiresByType video/webm "access plus 2 weeks"

  # HTC files  
  ExpiresByType text/x-component "access plus 1 month"

  # Webfonts
  ExpiresByType font/truetype "access plus 1 year"
  ExpiresByType font/opentype "access plus 1 year"
  ExpiresByType application/x-font-woff "access plus 1 year"
  ExpiresByType image/svg+xml "access plus 1 year"
  ExpiresByType application/vnd.ms-fontobject "access plus 1 year"

  # CSS and JavaScript
  ExpiresByType text/css "access plus 1 year"
  ExpiresByType application/javascript "access plus 1 year"
  ExpiresByType text/javascript "access plus 1 year"

  <IfModule mod_headers.c>
   Header append Cache-Control "public"
  </IfModule>
 </IfModule>

<IfModule mod_deflate_c.>
  SetOutputFilter DEFLATE 
  # compress text, html, javascript, css, xml:
  AddOutputFilterByType DEFLATE text/plain
  AddOutputFilterByType DEFLATE text/html
  AddOutputFilterByType DEFLATE text/xml
  AddOutputFilterByType DEFLATE text/css
  AddOutputFilterByType DEFLATE application/xml
  AddOutputFilterByType DEFLATE application/xhtml+xml
  AddOutputFilterByType DEFLATE application/rss+xml
  AddOutputFilterByType DEFLATE application/javascript
  AddOutputFilterByType DEFLATE application/x-javascript
</IfModule>