Prevent automated signups

[Davey]

I know one's already been released, but some people can't install it because their hosters don't allow what's required.
Therefore, I've devised a new method which should be just as effective, but can be used by all.
I thought of putting a checkbox at the start/finish of the registration form.
If when submit is clicked, the box is not ticked, it should not register the user, but spit back an error.
Is this possible? Thanks.

Dave.