Can a mask stick to a shape in the motion tracker? I have some video footage of a flat surface (for this example, let's say it's a binder or a book), and I want to digitally replace the cover of the book using a plane in Blender. So, I set up my tracking scene and align the plane and stuff and it attaches to the book. The problem is, someone picks up the book, so their hand is now covering part of it. Is it possible to draw a mask that will conform to the shape of the hand, or something similar? Maybe like a lasso tool (like they have in photoshop) or something similar? Or will I have to adjust the mask frame-by-frame?

Thanks. :)
The mask control points can be controlled by trackers.
So track the hand (or the edges where the hand moves over the book cover) and parent those trackers to the mask.

To do that select the mask's control point, then shift-select the tracker to control it and press CtrlP. Now the control points will follow the tracker automatically.