[Vince]

You can use a GeoIP solution to block anonymous proxies but that probably won't catch the majority of VPN providers. Since you're talking about a website you can also cross reference the Accept-Language request header with the language spoken in the country the IP belongs to. Not 100% waterproof, but if the header is set to Romanian and the IP belongs to France then you can be relatively sure that something is amiss. If you want to process registrations manually then you can also do a reverse DNS lookup on the IP so you know what provider it belongs to.