Hi
At first, you have to think about the territoriality principle, i.e find the law(s) of which countries are practicable.
Secondly, you have to check whether the involved countries signed the Berne Convention (it’s trivial as almost all countries signed it), the Geneva convention, the Rome convention and others conventions of the World Intellectual Property Organization.
Thirdly, you have to determine the country of origin, often the country in which the content was published for the first time.
Fourthly, you have to find how the “fair” uses of copyrighted works are defined and implemented in the laws of those countries (the country of origin which often prevails and the country of the person using the copyrighted work).
Some countries allow to use some copyrighted works to inform people, in recent news, in parodies, in text and data mining. We speak about “fair use” or “fair dealing”. There is no homogeneous implementation of those principles in the national laws, I admit that it doesn’t ease anything for those who may wish to use copyrighted works.
Youtube has become particularly picky since the Content ID has been enabled. Numerous famous Youtube users who upload lots of videos containing copyrighted works prefer joining some networks. Those users share a part of their profits with them and they manage the juridical risks in return.
In my humble opinion, there is a clear distinction to do between copyrights and authors’ rights, I find legitimate that an author chooses a license for her/his creations as long as it doesn’t contain too much restrictions and I find legitimate that the people who’d like to use her/his stuff must respect the license, it’s the same for the source code as I would certainly prosecute someone who would infringe the license of my source code.
If there is no license, consider that the artwork is copyrighted. As the right to inform is quite protected in numerous countries (mainly on recent news, it becomes more complicated for other news), you can use at least some parts of copyrighted works only for this purpose but I advise you to obtain the prior consent of the copyright owners in other cases.
I know that tons of websites take lots of risks but I advise you all to take no risk in your projects. Sometimes, the copyright owners wait for months or years before contacting you and/or sending a DMCA/LCEN takedown/staydown notice, which was what happened Pokemon Safari (Nintendo waited 10 years) and T.U.E.R (Sega probably waited for several months). Nowadays, the corporations take care of their rank in search engines. Trademark registration is very expensive, protecting the registered trademarks on the long term is crucial and very expensive too. Nintendo has a long story of closing tons of fan websites, websites of clone projects (fake Super Mario 64 HD, tons of Pokemon/Mario fan games, …) and emulators’ websites (snes9x, GBA4iOS, …).