How to identify unique user?

Question

Question

How can you determine if a user is unique or not?

I understand there are many ways to do this using cookies, but what about methods that don\'t us

Answer 1

IP address is commonly used but fallible, as others have said. Note that AOL (and perhaps other ISP's) use shared proxy servers for content-type requests and caching, so that a single user's requests for images may show up to your server as coming from several different IP addresses. Conversely, all AOL users' requests for images will therefore comme from these same IP numbers.