Just 2 days ago, NASA unveiled a new Blue Marble "photo" of the Earth taken on Jan 4, 2012 by the newly launched Suomi NPP satellite.
Satellite photos are not captured in the same way as regular optical or digital cameras. What happens is that light from various bands of wavelength are captured by separate sensors. The data is then selectively composited in a way that would show "true colors" as they would appear to the human eye, e.g. taking the red, green and blue wavelengths and discarding non-visible wavelengths such as infrared. During the compositing stage, color correction can be done to remove the blue tint cause by atmospheric scattering of light to get the vibrant, natural colors like we see in this new NASA image.
To get high resolution imagery, the satellite must have low orbit, which means it will not be able to "see" the entire Earth in one picture frame. Instead, the sensors can only capture a small area of the Earth's surface at a time. As the Suomi NPP is a polar-orbiting satellite, it circles the Earth in a north-south orbit along the longitudinal lines, building up swaths of the Earth's surface as it orbits. Each orbit create a vertical strip of information. A global map can be stitched together when the entire surface of the planet has been covered in this manner.
Anyone who has stitched separate photos into a panorama will know that the process involves fixing perspective distortions and lighting inconsistencies. In any case, the completed map must then be projected onto a sphere to look like the Earth as viewed from a distance. Very few man made spacecraft has travelled this far away to be able to view the planet in its entirety. Even the ISS and space shuttles orbit closely at only 300-500 km above the Earth's surface.
Regardless of the technical manipulations necessarily to achieve the image, it is highly detailed and stunningly beautiful ^^
