Usually, when I'm developing websites which interact with clients, I used to use their usernames or user IDs to save their configs and so on. But now I'm developing a website with no login system and I need to save some things, like "likes", "Accessed pages" and more.

I've tried Internet Protocol (IP) but it won't work when the visitors are under NAT or Proxy.

How can I create an unique ID for every single user and them save it in my database?

By the way I'm using PHP.

This sounds like a recipe for disaster if you are trying to save user data long term.

I would recommend:

1. Create a random but unique hash and save that to a database.
2. Set the hash as a cookie on the user's computer.
3. Save all 'likes', 'accessed pages', et al. to the database keyed on the hash.

The problem arises when the user clears their browsing history/cookies and now there is no way to retrieve that user's activity because it's all based on that hash.

I guess one work-around would be to send an email to the user with their hash and instruct them on how to reinitialize their activity history.

You would have to create a special page where they could enter their hash and your system would reset the cookies on their system.