Your link is incorrect so nobody can see your example. youtube.com/watch... isn't going anywhere without the stuff that comes after /watch
If you want to replace one image with another, simply add your image to the scene and make it match the movement (if there is any).
You might be able to do keyframes by hand to animate the position, scale, and rotation. However, you might need to use some of the motion tracking tools that come with AE. Learn more about motion tracking here: After Effects Help | Tracking and stabilizing motion
If you want to change the faces in this footage then it's going to be very difficult because of the transparency and reflection problems.
The only way I can see to do this effectively would be to track each bubble then create a new bubble as a composite image complete with the moving reflections and the new face. It would be much easier to use C4D and Mettle's new Sky Box along with some stock footage and recreate the look from scratch. To get the reflections to work on new bubbles or to replace the existing faces and keep the reflections is going to be tough because blend modes that would keep the reflections in place would also blend the faces already in the bubbles.
That's my 2¢