This picture of Barack Obama is the first official presidential portrait ever taken by a digital camera. The details are in the EXIF data.
It was taken by Pete Souza, the official White House photographer, with a 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.