but if we take google for an example. they give the serached sites something in return, they make the easy to find. but how does the google spider know that it

but if we take google for an example. they give the serached sites something in return, they make the easy to find. but how does the google spider know that it can index the site? it checks for robots.txt obv but does it check for Copyright? http://en.wikipedia.org/wiki/Fair_Use http://en.wikipedia.org/wiki/Fair_Use fair user seems to be only in the US, i potentially want to reahc the whole world even if the USA is a good place to start.