You don't have to select points on a mask, necessarily, just points in general. What you want to do is select the points on the four corners of the CG painting plate. Click Four Corner in the Layer (Surface?) tab of the composite controls for the CG layer, then click the point selection mode button in the tool bar, and shift-select the four points at the corners of the CG layer. Now, when you click on the Tracker tab, it should say "Track 4 Control Points" when you select the background as a source.
Unfortunately, this is where you will run into trouble. You can certainly put the trackers on various objects in the room and set the track mode to Relative, but I'm guessing that the relative movement of the TV set, table, points on the wall, etc, are not going to give you the results you want (sticking the picture on the wall). If you have the option of re-shooting the background footage, it would be a good idea to put markers on the wall (white tape in an "X" shape works very well) in the place you want the four corners of the CG image to stay, and use those as your tracking references (rather than the corner of the TV, etc). Even better, so you don't have to mask the markers out later, put them just inside where you want the four corners (so the CG image covers them up when you track it on them) and track on Relative.
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Brian Demong
Publisher, Combustion Instructor
Mesmer Animation Labs