>it gets posted in the first 20 posts or so
They can easily adapt their behaviors.
The closest thing to a solution is to ban IPs. This would cause them to switch to VPN to make IP hopping easier. So most VPN IP ranges would have to be banned too. Short of that, the CAPTCHA frequency could be increased for those VPN ranges. I don't use a VPN; I I don't care. But I know a lot of anons still have redlist/bluelist fears and (adorably) think Tor and VPNs provide a degree of anonymity.