Mr. Harryhausen strove for realism. He constantly sought ways for his creations to share the screen and interact with live actors and settings as seamlessly and believably as possible.
The heart of his technique was a process he developed called Dynamation. It involved photographing a miniature — of a dinosaur, say — against a rear-projection screen through a partly masked pane of glass. The masked portion would then be re-exposed to insert foreground elements from the live footage. The effect was to make the creature appear to move in the midst of live action. It could now be seen walking behind a live tree, or viewed in the middle distance over the shoulder of a live actor — effects not possible before.