yeah, in the U.S. many people have been caught by that sinkhole. Not a negative spin, I'm an artist and personally I agree with it. In one case I recall a contest winner needing to return the $250,000 prize for a full colour illustration based upon a black and white photograph of an aboriginal man wearing a traditional headdress. The likeness could be seen. Thus.
In my experience the only rule of thumb one can follow is to be your own artist, though incorporating elements that you find pleasing or helpful into your own personal creative world is normal. I believe it's the important to re-imagine and retell, whereas you take what was put out there, and use it to tell your own story. Otherwise Battlestar Galactica would be illegal. Which most agree would be bad.
though I may be proven wrong if Lucasfilm follows Facebook into the abyss by suing all others with the first name 'Star'.
the artist formerly known as Bongo51