It's taken at the Nürburgring if I am not mistaken. Karoussel corner.
As u may know, there are quite a few professional photographers who mainly do NBR and cars, and I would think that the picture is taken by one of them - unless you know for certain that its an official Porsche picture?

Check www.touristenfahrer.de or do a search on Yahoo! or Google on "nordschleife foto" or "nordschleife touristenfahrt fotos".

Good luck