Pretty sure I see the button on your screens, it's on the wall where others show you the painting. Hard to see from above, you probably want to look sideways (it's far more obvious in screen 3 than the first 2).
Yep, I see it too.
Press the button and the trapdoor will appear. You don't have a picture on the wall anymore because you looted it BTW.
I probably did destroy it while ransacking the room, it was too long ago so I don't remember very well.
Anyhow, I managed to find the button(some camera rotating was required)
Thanks everyone!
Well, you do not need to finish the Black Cove at all - it is completely optional! If you are having troubles in the Luculla Forest try quicksaving during combat (when you feel like you have an advantage). If you think you are on the verge of loosing the fight, then reload the previous quicksave. Yes, I know it is a little bit of a cheating but Black Cove probably won't give you enough XPs to level up anyway (Pontius Pirate is level 6 or 7).
Well, Ive been playing blind up until this point, so I didn't know that is was intended for the player to be underleveled in Luculla, hence I assumed I had missed something major.