a.k.a. morphing, made popular in the early 90's it still find uses today
The morphing module is a .so file that can be loaded into the TclTk wish interpreter. A simple script presents the user with an interface through which the module is utilised. The user specifies corresponding features in the starting and ending images, the interpolator fills in the rest.
The resemblance is uncanny. See the sequence as a 37K MPEG-1 movie.
Another example: a very presidential primate from the Bush-or-Chimp site.