In this plate she walks over and sits on a chair. To replace the green screen prop with a CG chair a matchmove was used to match the plate with the CG environment as well as provide some feature tracks on the green screen chair. These features were used to obtain the correct positioning of the new chair.
The biggest problem with this plate was the huge amount of green spill on the actor. Normally this would be minimised by using spill suppression techniques e.g. black cloth etc. The result is that the procedural matte is a little extreme!
Check out the results....

The source video sequence for this shot is from Hollywood Camera Work.