Google Page Speed complains about following file (Leverage browser caching)
http://dy2em7yqysbvb.cloudfront.net/images/flags/az.png (expiration not specified)
In my browser file already come from cache with 304 Not Modified HTTP STATUS CODE
I use Cloudfront cdn service of Amazon and my settings are shown below
The configuration you specify here controls how CloudFront caches objects, not how they are cached by browser. You still need to send Cache-Control header from origin to control browser caching.