Iâ€™m not 100% sure this is correct, if Iâ€™m wrong I would be glad if anyone corrected me.
From what I have gathered, to be on the legal side you need first of all a CNAPS authorisation â€œagent de recherches priveesâ€ (= Private investigator) to take part in Surveillance task, and you need also to work with a proper â€œcontrat de travailâ€ (direct employed with all relevant paper in order) for a company that have authorisation from CNAPS to perform private investigations.
Other than that it pretty straight forward
As prescribed by the Code of internal security, no one can practice individually a private security activity or direct, manage or be a member of a legal person exercising this activity, if not holder of authorization by the CNAPS.
activity of private research can not be combined with any other private security surveillance or guarding, transport of funds and protection of the physical integrity of persons (Article L. 622-2 of the ISC).
Surveillance operations are overseen by a nine-person committee led by Prime Minister Manuel Valls. But that committee has only an advisory role, and cannot overrule decisions by the prime minister.France passed its controversial â€œIntelligence Bill,â€ allowing it to increase its surveillance powers. Now, in the wake of the devastating terrorist attacks that have left Paris in mourning for the second time this year, itâ€™s worth re-examining how the law might be put into action as intelligence-gathering accelerates.