Ok folks, just changed my mind (happened before also many times in my MR “career”…), instead of modelling a Zm Swiss layout begun working on a Z scale US modular layout. Concerning my first module, I had allready attached a swiss backdrop photo with white glue to the wooden backplate. Just tried to rip it off, but as it is a photograph, I just manage to remove the outer layer and the paperbased underlayer stays there 
Anybody knows a quick way to neatly remove the backing paper? I first thought of soaking it with water but I hesitate because of the risk of warping the back panel… Appreciate your feedback!
You might try steaming and a putty knife. Do a little at a time. Good luck!
Heck I’d just place a thin new layer of masonite over it and put the new backdrop onto that…lot less head aches.
Sand it off (it’s only paper, you should go through it fairly fast) or, if it’s flat enough, just put the new picture over top if that’s an option. Depends on relative sizes and shapes, of course.
If its anything like wallpaper use a spray bottle with warm water and a puddy knife. You might also try wallpaper remover solution found at paint stores.
Thanks for the input, I think I’ll sand the remains off and attach a new background.