Two of the basic assumptions the authors mention include 1) the background is stationary and 2) camera motion is handled if it is parallel to the plane of the image.

If the background is far away from the foreground object (like in their outdoor examples), you can approximate it as stationary, but if the background isn't very far away from the foreground object (indoors), it will not be stationary with camera motion. In this case is their assumption violated and their algorithm unusable?