Added browser caching over my #snac instance, for better user experience with all the files being proxied from other instances. Apache configs (requires enabling mod_headers if you don't have it already):

    <If "%{REQUEST_URI} =~ m#^/[^/]+/(s|x|y)/.+$# || %{REQUEST_URI} =~ m#^.*\.ico$#">
        Header set Cache-Control "max-age=172800, public, immutable, must-revalidate"
    </If>

The last .ico part is not necessarily snac related obviously :3