Dear Henk, thank you for this very interesting picture.
There is a very interesting book written by Alessandro Sannia called 'Fiat 850 Fuoriserie' about Fiat 850 derivatives, including a big number of Formula 850 cars. Sadly, there is no Martini F850 in it, but judging by the pictures of other cars from that book I can tell you that this picture was most probably taken at 1967 Saloncino dell'Auto da Competizione di Torino, and the car in a background is a Sozzani F850 built by Fidenzio Sozzani.
The wheels and suspensions of a Martini look quite similar to the ones used on Formula 850 cars (and not similar to Tico Martini's cars' suspensions in my opinion). Can't be sure for the engine though from this point of view.
Also, even though the nose is quite similar to Tico Martini's cars, the emblem looks different to me - the French Martini did not use a round shaped emblem as far as I know. Martini as such is an Italian surname, so for me it is not impossible that some guy named Martini could have built an F850 car on his own. On the other side, I'm not a specialist in French formulae, so maybe this is some early car by Tico Martini which I have never seen before (although I'm nearly sure it is a Formula 850 inded).
All the best,
Alexander