Hello!
All files need a valid license and information about the source and author. I checked a few and it seems most files have a license so that is good. This beautiful file does not have a clear source and author: Ficheiro:Paisagem da praia.jpg
It is not in use so it can be deleted without leaving a blank spot in any pages.
There are 97 unused files at Especial:Ficheiros_não_utilizados it looks like they are very old so I wonder if they will ever be used. Perhaps they can be deleted?