This paper describes the image processing algorithm which aims at determining the fragmentation size distribution of copper ore elements placed on a moving conveyor belt. The system utilized to capture the passing elements of the ore is the laser profiler. This system sends a laser beam which bounces against the monitored structure and returns to a receiving part of the system. In such a way a kind of a topological map of the monitor scene is created. The algorithm takes this data as an input and processes it for determining the boundaries between different ore elements as well as between the elements and the conveyor belt surface. Once determined, surface areas of the ore elements are calculated and a resulting fragmentation size distribution is obtained. Apart from the description and performance of the algorithm, the paper summarizes the disadvantage and advantages of the developed image processing solution.