Here is some of the work he has done.
The Dynamation that Harryhausen did was very time consuming and particular. It combined the foreground and the background images. To do this, he photographed miniature creatures in front of a projection screen or sometimes through a partially masked glass pane. Later he would superimpose the live footage on the part that was masked. The way he balanced the lighting and color was flawless. Because this was before green screen it was amazing and was something no one in the business had ever seen. His work and contributions to special effects and animation play a large part in why and how we are capable to do what we can do today.