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?