Hi Stig,
With regard to the type of aircraft shown I've let myself be swayed by
http://albindenis.free.fr/Site_escad...ete_Farman.htm I assumed that this was probably the photo referred to as his source given that the aircraft shows 218 and Chartres is written below the photo. But I agree with you, this is a MF.7.
As for whether this is the aircraft serial we're seeing, frankly its impossible to say. Hopefully at some stage photos of a Farman turn up showing both the inside of the cockpit and the serial onthe tail. Well I can dream...
Thought it worth posting the image in any event because of the unusual location of the number.
Regards,
Clint