As you may or may not have noticed, okws.org runs on the Apache Web Server. (We've also recently ported okws.org to a PHP-based Wiki, which is really cool software.) Unlike typical Web servers, OKWS is specialized for dynamic content and is not well-suited to serving files from disk. Sites that use OKWS therefore rely on typical Web servers (such as Apache) to serve images and other static content. In the OKWS paper, we argue that the separation of static and dynamic content across multiple machines running different servers is natural and contributes to overall Web site security.
It is possible to write OKWS services that serve static content, although this technique is currently not as convenient as just using a server like Apache. Future versions of OKWS might include better static content support.
Lighttpd is a web server that is especially well suited for serving static image files.