Hi,
I've just checked in a smart solution for the problem: if a user has
already solved a captcha, his author name is stored in a session
attribute and all captchas are omitted for the session lifetime. A
side benefit: the user has to enter his name only once.
You can exploit this feature also for your use-case: simply store an
empty string ("") in the session attribute (JEASE_DISCUSSION_AUTHOR)
to omit all captchas in discussions for your site.
HTH, Maik