I was thinking about questions like that too. In printed works you are allowed to quote other printed works. So if you quote text from a book or a picture of an exhibition in a magazine article about the book or the exhibition this is ok -according to German copyright which is similar to French and in general continental Europe copyright. (Of course quoting the whole book would not be ok...)
So a quotation should be ok online too -if you mention the owner of the copyright.

But copyright law is complicated stuff.