Yes, this picture is a composite. The day/night boundary is not so sharp in reality.
Some cool links for pictures are:
http://edc.usgs.gov/ - this is the top page of the USGS Data Center, lots of links. A clearinghouse of sorts.
http://edcw2ks15.cr.usgs.gov:8090/Im...ondisplay.html - this is an image colection. Check out the "Earth as Art" collection.
The next two links I look at every day, sometimes they have satellite pictures. Archives are available.
http://epod.usra.edu/ - this one shows a different picture related to Earth Science every day with explanation. The above photo was displayed last month with explanation.
http://antwrp.gsfc.nasa.gov/apod/astropix.html - this one shows a different Astronomy picture every day with explanation.