how detect that a visit to my site is done by a search engine and not by human? the referenceUrl (visitor come from) is always null if search engine auto visit or...? I know to get server params like ip, reURL, etc

why do you need to do that?
it is easy to recognize google bot
try playing around with robots.txt

I want to filter list of visitors by Real visitors or search engine in Admin Panel of the Site, well?

Any reputable search engine will provide details of the company in their user agent string, use $_SERVER['HTTP_USER_AGENT'] to check this. There is plenty of information online with lists of search engine agents.

Even going to google and entering the exact title of this thread brings up enough information that you should be able to work out where you should be looking.

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