For example is there any servers with photos with Creative Commons licence? And not only some general photos but, with concrete objects (people, buildings, pictures etc.). And if I find a picture on a site (for example search in Google) how can I find its licence? I am interested especially in photos or famous people, but not only that.
If not stated differently, websites contents (this including photos) must be considered copyrighted by the owner/maintainer of the website and you can't use them straight away.
It is always a good (and nice) thing to ask the owner/maintainer for licence term and/or permission to share that photo on Wikipedia.
Google allows to filter the results based on the licence (append to the URL the following
&tbs=sur:f ) but also stated "Images may be subject to copyright." so you shouldn't exclusively rely on it.