identifing computers
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I want to identify visitors computer and track it.  I log visited pages. For example when you visit my webpage i'm generating md5 hash of your ip and send it to you as a cookie .  And then when you browse to my pages i'm logging every page with this cookie's value. So,  when you visit my webpage tomorrow,  i can tell you,  *you visit these pages yesterday :* 

But if you change your ip, i'll lost all informations about you. 

What can i use instead of IP ADDRESS for identify computers? 