Thanks for the clarification.
If there's no immediate way to prevent the spam, I'll happily keep reporting it, and hopefully it it'll die out eventually.
I don't want to suggest you reinvent the wheel, but another forum I've been part of for years has a very good way of approving new members, which I think would go some to prevent this sort of thing. Rather than just a series of tickboxes, drop down menus and an image verification step, this other forum requires a more pro-active effort on behalf of both the user and the moderation team. The new user is required verbally state certain things like the fact that they have read, understood and agree to the rules, provide their name and location, and a little bit of information about themselves (age, hobbies, cars they drive etc). This then goes to the moderation team to approve before the user can post on the forum.
Requires more effort on both parts, and some users do whinge about this, BUT, I think if that sort of process was in place here, the spammers would be easy to spot at the first step.
Something to mull over anyway.