Well, the same criteria of the Berne convention apply, meaning that the idea has to be expressed under any form in order to be protected, because mere ideas can never be protected by themselves, and the work has to be original, meaning it must express the author's personality. So I think porn is kind of likelier not to fulfil those criteria. However originality is extremely difficult to define and has to be assessed on a case-by-case basis.

The real question is if there is any kind of morality clause or something like that preventing porn from being protected, and there isn't under the Berne Convention, but the US constitution contains the Copyright Clause, saying that Congress my protect intellectual works that "promote the Progress of Science and useful Arts", upon which the aforementioned District Court filing relies. There is no equivalent in Belgian/European copyright law or international law governing or superseding Belgian law. Therefore I thought it would be kind of interesting to use the DC case as an introduction. It's more like an anecdote than an important legal scenario.