The FIA regulations state
20.1 Presence of cameras and camera housings: All cars must be fitted with either two cameras, two camera housings or one of each at all times throughout the Event.
20.2 Location of camera housings: Camera housings, when used, must be fitted in the same location as cameras. Details concerning the size and weight of all camera housings may be found in the Appendix to these regulations.
20.3 Location and fitting of camera equipment:
20.3.1 All cars must be equipped with six positions in which cameras or camera housings can be fitted. Referring to Drawing 6, all cars must carry a camera or camera housing in position 4, the position of the remaining camera or camera housing will be determined by the FIA after consultation with the relevant Competitor.
There's a little more, but basically they have to carry a camera above the roll hoop/air intake, and then the rest is up to Bernie and his boys.
http://www.fia.com/resources/documents/ ... ATIONS.pdf