How to detect new Machine like Facebook?

Question

I am actually trying to detect a person, using a computer, Just like facebook. Whenever you sign into facebook using different machine, it detects the new machine and asks you t

Answer 1

This process has very little to do with cookies, it's called fingerprinting.

Basically, you can look at the functionality and support of your browser and there is a likelihood that the combination will be somewhat unique.

You can test this out here: https://panopticlick.eff.org

JavaScript example, but the theory can be transposed to any language: http://valve.github.io/fingerprintjs2/

Using this in combination with cookies is the best way to detect unique devices. Store the fingerprint in a hidden field when you login and check that against the available fingerprints you've already got.