The evidence looks pretty damning, as you can see from these two screenshots of different Microsoft sites. The first is its main US site and the second is its Polish site:
Screenshots taken from Microsoft’s English site and Microsoft’s Polish site. As you can see from the full versions on those sites, the person’s hand is the same in both and it is the first (US) one that looks to be the genuine photo.
UPDATE: Microsoft has now apologised: “We apologize and are in the process of pulling down the image”.
UPDATE 2: Here’s the story from the BBC.