> We could have 10 or 20 alternating images for the human author
> to recognized and include as part of the verification process.

Unfortunatly, the bot programmer could easly have their bot try 10 - 20 words on
every page. The human hacker could discover all the words after a few minutes
at the site.

You'd need a couple thousand words at least, randomly selected.

Cheers,
Darius