From Time Machine
The twin NASA MODIS satellites image the earth daily in many wavelengths, and the two satellites have been collecting imagery since 1999 and 2002.
NASA Earth Observatory's Blue Marble imagery shows the color of the surface of the earth for each month of 2004, at very high resolution (at full zoom, each pixel is 500 meters wide). Because any given day's imagery has many clouds obscuring the surface of the earth, much of the work in generating this dataset was determining for each location what it looked like without cloud cover.
Paper describing how Blue Marble was created.