Oh sorry...
I just meant, that the reason for using these security images is only to prevent spam-bots from registering on your site and posting to your forums.
So if you allow public write access to your forum, they won't need to register to write their stuff and we're off with less registered spam bots.
But of course, this suggestions is not meant to be taken serious.
I too think that these images would not only be a valuable addition to CB but instead a very much needed, mandatory feature in these days...