"This module equips a Web server with the same functionality provided by motd. Once the module is installed, the administrator can configure the Web server to display the message of the day to every user accessing any Web page on the server. It momentarily intercepts the initial request and displays the contents of the motd file, then the user is redirected to the originally requested document. The initial request also sets a cookie so that subsequent visits are not directed to the message of the day"
"Although Apache::Motd was originally intended to propagate important messages to our Web community, I have found other interesting uses for it. For instance, you can add a "Terms of Usage" screen to an existing Web application, without having to modify any existing code."
A while ago I toyed with the idea of writing a generic mod_perl handler (which could be contributed to CPAN. This module (too be called Apache::HumansOnly) would be extendible in the Apache::HumansOnly::* namespace. Essentially the idea would be for advanced protection against web spiders (good and bad), without requiring registering. For example, there could be one module that uses Image::Magick to generate an on-the-fly image for first-time users, getting them to read a word embedded in the image, and type it in to the text field. My main goal was to make it extremly simple for valid users (like me) to do things like rollback pages in this Nyetwork MiniWiki-based site, but not let the well-meaning indexing spiders follow the links to rollback to previous versions.
Anyhow, while going through the list of pages, I discovered Apache::MOTD (already linked in the Perl page), which should do exactly what I wanted. Just need to set up a '<Location>' directive in httpd.conf, which will hook into the HTTP request phase before MiniWiki is.
see also Perl