I am trying to impose an image on a video, I made the mask and the alpha over with the video, image and mask, but it shows up like this:
Also, How can I get a mask to display multiple images, like a slideshow?
The reason it is not working like you expected is because you are using a mask. Right now all you are getting is a black and white mask that has no transformational information so all it is doing is "hiding" the part of the image outside of your mask.
What you want to do is use a Plane track and a Plane Track Deform Node. After setting up the plane track, that node will deform whatever image you give it as an input to match the skew of the plane track.
My answer here show the whole process of setting up the track and the needed nodes in more detail.