Anything in public space, anything visible from public space (at least with the naked eye), can be photographed without permission. People have no title to object against being photographed. They can have a temper tantrum, but that should not impress you.
While this is also based in freedom of press and news gathering, in my country there is an option for people who have been photographed, to object against publication. This would require a special high-speed court case where the judge must agree with the matter's urgency before the trial. The essence is that a "reasonable personal interest would be damaged/harmed". Without such a case the photographer by default has the right to publish and needs no consent. In recent decades, some countries may have made an exception when minors (children) are involved. But rendering a child's face unrecognisable may be enough in that case.

The question is what laws apply in Monaco. Considering the magistrates in the legal system are French, the differences with France will be small.