Distinctions like this are rather fuzzy, but I think this sits the other side of the line most people would draw then the pages you mention.
(For reference, dear reader, in case the pages changes between me writing this and you reading it, the linked page contains stills from Back To The Future used as background images.)
Some parts of HN don't make that kind of meta style comment because it's off topic for HN. But here it's a risk for the site owner - DMCA could remove their site - and so people mention it.
There are people who could mention copyright at every applicable opportunity and I'm glad that they don't. (Although I would like a place for that kind of comment! Also, tpyos).
ETA: also this is completely ignoring any relevant international laws. French law, which is where the OP lives, appears to provide some protections for "necessary" use.
"The Court of Appeal disagreed and applied French law. Nevertheless, it too rejected plaintiff's claim and decided that Google benefited from the "safe harbor" provisions of the Loi sur la Confiance dans l'Economie Numérique [the relevant French statute]. It considered Google as being a "neutral" actor and the reproduction of the photos necessary to provide the service."
http://cyberlaw.stanford.edu/blog/2011/01/who-said-france-do...
Necessity isn't a criterion for fair use, it's the reason fair use provisions exist in the first place.
Making satire of or discussing a copyrighted work without using copyrighted material is extremely awkward if at all possible. Internationally speaking (i.e. aside from the specific definition of fair use in US law), necessity is a good rule of thumb, just like profit/non-profit use.
You don't have a license for those images, so you can't use them. Period.
Fair use only applies under certain circumstances where using copyrighted materials is necessary (e.g. satire or discussion). Even if you don't use them commercially, you can't just use them like that.