Hi, As far as I understand the text content is stored on the blockchain itself and that is stored on many decentralised servers some witnesses use AWS as far as I know but some have their own making it quite decentralised. Image etc. may be stored on centralised servers but I am not sure if they are mirrored. Maybe someone else can weigh in on this.
RE: Hardfork 24 update: testnets and hivemind progress