Morhing

Morphing is a special effect in motion pictures and animations that changes (or morphs) one image or shape into another through a seamless transition. Most often it is used to depict one person turning into another through technological means or as part of a fantasy or surreal sequence. Traditionally such a depiction would be achieved through cross-fading techniques on film. Since the early 1990s, this has been replaced by computer software to create more realistic transitions.
Though the 1986 movie The Golden Child implemented very crude morphing effects from animal to human and back, the first movie to employ detailed morphing was Willow, in 1988. A similar process was used a year later in Indiana Jones and the Last Crusade to create Walter Donovan's gruesome demise. Both effects were created by Industrial Light & Magic using grid warping techniques developed by Tom Brigham and Doug Smythe (AMPAS).
Three frames form a morph from George W. Bushto Arnold Schwarzenegger showing the midpoint between the two extremes