Expires Headers Not Working

Question

On multiple SEO tests, I am getting a response that

Your site is not using expires headers for all of your images.

However, this is a part of my .htaccess:

htaccess

# Expires Headers
<IfModule mod_expires.c>

    # Enable expirations
    ExpiresActive On

    # Default directive
    ExpiresDefault "access plus 1 month"


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

    # Images
    ExpiresByType image/gif "access plus 1 month"
    ExpiresByType image/png "access plus 1 month"
    ExpiresByType image/jpg "access plus 1 month"
    ExpiresByType image/jpeg "access plus 1 month"

    # CSS
    ExpiresByType text/css "access plus 1 month"

    # Javascript
    ExpiresByType application/javascript "access plus 1 year"

</IfModule>

Here are the headers:

Reponse

HTTP/1.1 304 Not Modified
Date: Mon, 29 Jun 2015 09:25:36 GMT
Server: Apache
Connection: Keep-Alive
Keep-Alive: timeout=2, max=100
Expires: Wed, 29 Jul 2015 09:25:36 GMT
Cache-Control: max-age=2592000
Vary: User-Agent

Request

GET /img/tap-logo.png HTTP/1.1
Host: tap.#######.com/
Connection: keep-alive
Pragma: no-cache
Cache-Control: max-age=0
Accept: image/webp,*/*;q=0.8
If-Modified-Since: Tue, 16 Jun 2015 12:23:44 GMT
User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/43.0.2357.130 Safari/537.36
Referer: http://www.#######.com/
Accept-Encoding: gzip, deflate, sdch
Accept-Language: en-US,en;q=0.8,en-GB;q=0.6

Why is this not working, and how can it be fixed?