Can anyone recommend some guestbook software that's relatively simple to set up and includes some form of verification (where an image of characters is displayed and the poster has to type them in)?

I've had a lot of spam on my current guestbook and it's also buggy. Normally I simply delete the spam, since all posts have to be approved. But recently some spam was posted which managed to approve itself.

I'd like some better software, even if I have to pay for it. I'd also like the ability to transfer the messages from my old GB, with their original date of posting (even if I have to enter the messages and the date myself).