Found some sites claiming it to be a shot of the F2 project, but I'm skeptical, everything just seems like hype and rumors on random blogs with nothing from McLaren themselves or sites like Autoblog/Jalopnik/etc. The source says it is a prototype, however the totally opaque windows suggest otherwise. Judging by the timing those pictures hit the internet (2008), I'm pretty sure they actually are leaked early studio models of the then-upcoming MP4-12C.
Granted, at the time, McLaren may have been intending to call it the F2, with the naming switch happening last minute. The intenrnal code for this would have had to be P11 (P7 being the SLR McLaren, P8-P10 being Mercedes projects cancelled in 2005), which in the end hit production as the MP4-12C.