It was taken by Pete Souza, the newly-announced official White House photographer.
It is the first time that an official presidential portrait was taken with a digital camera.
You can download the Hi-Res photo here: [link]
Camera: Canon 5D Mark II
According to the EXIF data, it was shot last night at 5:38pm. The settings: 1/125 exposure, F/10.0, 105mm focal length, ISO 100, no flash. You can download the full-sized photo here.
[from Gizmodo and Change.org]