The image, dubbed Blue Marble 2012, is actually an update of a similar image that was taken in 200s that has been the default background for the iPhone since the first one. The new image was taken with NASA’s new Suomi NPP satellite. To get the image the satellite took multiple passes around the planet on January 4, 2012. Those passes were then compiled in the wonder 8000 x 8000 photo you can find here. NASA also has other resolutions on it’s Flicker page, like the 640 x 640 one above and the 1024 x 1024 version that’s perfect for your iPad.