plugins - How can I add Expire headers to images? in WordPress

This can be done with Apache configuration, I have used this snippet in the past in .htaccess:

ExpiresActive On
ExpiresByType image/gif "access plus 1 month"
ExpiresByType image/png "access plus 1 month"
ExpiresByType image/jpeg "access plus 1 month"

Can be set up with plugin as well. W3 Total Cache (which I currently use) can do that among other things.

Overall this ist a huge performance factor. Modern browsers are smart enough about caching images even without expires set.