Basically you´ll have to check how the photo level feels. I would apply CW
rotation in tiny fractions (0,2 or 0,3 I would say) until you see it´s level. You can take the post below the tail of the aircraft as a reference. Not as a vertical reference, but just to get an idea of the level.
"Faithless is he that says farewell when the road darkens." J.R.R. Tolkien