I think it's a Mercedes W25 from the 1930's (it's in Toca Race Driver 3
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)
Also, that's clearly an 2005 MP4-20 in Macca's 2006 colours, but, as I often see in promotional photos, the front wing looks too close to the ground to have been in compliance for the aero regs 2005-
Hardly important, but it bugs me...
EDIT:
Actually, I think that Merc looks even older than the W25, doesn't quite look as aerodynamic, could be wrong though.
Still, I think the W25 is the best known car from that time, so it would make sense for them to use it... I dunno.