I found this picture in Wikipedia (its copyright expired so it can be reproduced here):
The caption says:
Execution of Prince Ratsimamanga and the Minister of the Interior under order of General Galliéni for having resisted France's annexation of Madagascar. Picture published in the French magazine L'Illustration, November 22, 1896.
This seems to be the aftermath of the Second Madagascar Expedition (1894-1895), a French conquest of the previously independent Madagascar.
Interestingly, the execution seemed to be carried out openly, a depiction of it is published in French magazine, and under official orders. The victims were a prince and a minister of a previously sovereign country, and the crime was "resisting France's annexation".
Did the French consider this execution legitimate? Were there laws against resisting France's conquest? How did the law get introduced and how were they applied? For example, France also conquered a lot of countries under Napoleon and it didn't execute their governments for resisting it.