identify unique users without authentication

Question

so my site has a feature that I intend to only allow to be used for a limited number of times per unique user...the thing is...I want to do this without having to force users to register and login to the site...

I was thinking of using IP addresses, but then IP addresses are easy to manipulate (with dynamic DNS, proxy servers etc)

So my question is, is there a method that is more reliable than using IP addresses for identifying unique users without forcing them to register

also I'm using the LAMP stack + JQuery so any solution that use them are welcomed...

Answer 1

These are evil, and your users will hate you, but here ya go:

http://samy.pl/evercookie/