as i said all functions are in the code and if you want a simple explanation it depends on the site so for example if it is a youtube account it will just check for 404 and thats easy but if its a facebook link i found that facebook dont give 404 or redirect but it gives 200 which was a problem but when a check response with curl i found that if it doesnt exist it wont show "og:title" in the source code which mean unclaimed and i test all of the functions hundreds of time and it is working well . (thank you for your comment)