DigiMatte or MattePainting has changed so much that artists create most of their stuff not only by using photos but as well as making everything from scratch. Speaking from an ILM digimatte's point of view. For a shot, you build your own asset, UV it, texture, light it, paint on top of it, make renders and lastly comp it in real well to sell your shot.
this is a personal digimatte, with a concept of making a military base, has started this one since Feb 2011, and working on it every free time after day time work.
WIPs Blocking
modelled a tank and Heli to fill up the scene, and some animatics
Build and Build
some renders to come . . .