The new Captcha system seems to be working like a charm, Kumori!
I had my doubts right away, since the day after it was implemented the spam happened again. The difference was that it finally had text in the post box, which I spamlisted. That ended up catching them the next time they tried three days later. Hasn't been a post or attempt since, but if the board starts catching it on its own due to the spamlist some more, I'll feel a lot better.
And as of today they've gone back to not having spamlistable text. At least we had a nice week of no spam though.