First of all, I would like to thank you all guys for providing best help that you definitely would not find elsewhere.
I have done exactly as you suggested include("(/var/www/vhosts/example.com/httpdocs/includes/templates.php"); and it worked for me.
I am not quite familiar with second option that you have also suggested dirname(__FILE__). I just do not know how to apply this method. If you can explain in little more details, would really help.
Thanks for your help, is there potential risk of security in the method that you suggested? For instance some pages on my site can be visible when you searching bing images, since it shows origin of the picture (meaning web page where this picture is located). Would this not mess it all up?