found yesturday, some clue where hidden by invisible UV paint ! that's why you had to be physically in front of it.
The one who found it promote by the way his company
The words were encoded - I still don't figure how - and where french words for banker, wear, lie, people, fight, hope, union, citizen, drive, triumph, horizon, yellow.
It was a good idea, the painting is also reflecting the mood of the time in France, the Liberty Leading the People is not topless anymore.
For the next time, I'd like a more universal riddle.