NPR's Mike Memmott explains how it was done:
The "Blue Marble" image of Earth snapped by the crew of Apollo 17 in 1972 is one of the most famous photos ever taken. When it appeared, we all suddenly saw the world in a much different way.
In the years since, NASA has added other "Blue Marble" photos to its collection, and has used technology to enhance and sharpen the images.
Today the space agency unveiled what it's calling the "most amazing high definition image of Earth — Blue Marble 2012." This one was taken "from the VIIRS instrument aboard NASA's most recently launched Earth-observing satellite — Suomi NPP," NASA says, and is a "composite image [that] uses a number of swaths of the Earth's surface taken on January 4, 2012."
Here a slideshow that adds previous views that include most of our home places: