Well I've investigate a little bit and I've found that also with the Bepeg4d solution the background image don't fit exactly the screen.
I've found a solution that it's really "dirt", tweaking a lot on 3d transformation value, so I ask if is possible that someone of the Octane Guru can publish an "How to do " guide, because as I wrote before, every day, expecially doing architecture rendering, we have to put a background image under windows or balcony glass railing, or simply viewing post effects of a light street ...