Well, funnily enough, I just went through the same thing. Now what I am telling you is more than likely the wrong way to do it but it worked for me in this instance. If I use terms that may not be absolutely accurate, I apologize but I am going off of memory as I do not have the file or software with me.
So, The firt thing I did was do a motion tracker with the four track points on an area that is always in the scene.That means the track points are not all the way to the edges of the area to be filled/replaced. I brought in the footage/image that needs to be tracked. I took the four first motion track points from the original footage that I did first and applied it to the image that needs to be tracked/pinned. I then precomposed the image. No… I think I precomposed the image first and page sure the anchor points made sense with the track motion points.Then I applied a corner pin to it and added the track points to the four corner pin points. The image is obviously smaller than what I wanted but what I did to correct that is co into the timeline that was precomposed and simply scaled it up until it fit properly in the final comp. I returned to the final comp and rendered it out. I was perfect. Now chances are I did a lot of crap but the crap worked for me. LOL. Try it.
Cheers,
JJ