The cluster computing is widely used for image processing in entertainment applications. Measuring the required number of nodes to be used in a cluster computing helps saving nodes processing time, even if this occurs on a fault-tolerant scenario. The paper analyzes the images rendering process by ray tracing on the cluster computing using the freeware software fault tolerant message-passing interface with Povray software in a Linux-based operating system. This paper uses a simple method of image complexity measure; it is shown that depending on the images complexity level, a minimum number of cluster nodes is chose to render the image instead of using all the cluster nodes. It is useful to save machine processing time and meanwhile another image can be rendered in a parallel process with a previous one and where the solution is applied in a Fault Tolerant scenario, so independent of the network fault, the cluster continues working. © 2010 IEEE.