thanks but that is replacing the face with another video of a face
is there an easier way of doing it with just a photo?
Exact same technique. Track the face, add a photo, apply the tracking data to the photo. This is really basic stuff.
You'll still need tracking information to make sure that the photo-face sticks to the video-face.
You can use the basic Ae Tracker (position/rotation), and apply the resulting tracking information to your photo (or to a NULL which you can use as a photo-face parent).
Use the After Effects tracker, not mask tracker, not camera tracker, but tracker to Track Motion of a face. Pick something prominent like the eyes and nose. Now add a null to the timeline and in the track motion panel select the null as the target and apply.
Now add your photo, move it into position and scale it to fit, and then, in the parenting column of the timeline make the null the parent of the face layer.
If you have no idea what to do when following these instructions then please research the help files for correct motion and parenting. After Effects is a very complex program that you cannot successfully use without taking the time to learn how it works.
that worked easy as