 McCay 's working methods were laborious . On Gertie the Dinosaur an assistant painstakingly traced and retraced the backgrounds thousands of times . Rival animators developed a number of methods to reduce the workload and speed production to meet the increasing demand for animated films . Within a few years of Nemo 's release , it became near @-@ universal practice in animation studios to use American Earl Hurd 's cel technology , combined with Canadian Raoul Barré 's registration pegs , used to keep cels aligned when photographed . Hurd had patented the cel method in 1914 ; it saved work by allowing dynamic drawings to be drawn on one or more layers , which could be laid over a static background layer , relieving animators of the tedium of retracing static images onto drawing after drawing . McCay adopted the cel method beginning with The Sinking of the Lusitania . 
