Are these two different problems? If so, explain them further so readers can understand more clearly.
If you're asking, can you use a black and white monochrome image as a mask / matte? then yes, you can.
Place the b&w image above your footage in the layer stack and then set the track matte of your footage to luma matte or luma matte inverted, depending whether you want to see through the white or the black.
Simon Bonner
youtube.com/simonsaysFX