A method is provided for controlling the operation of a machine for harvesting root crop. At least one optical image-capturing unit captures at least one test image of harvested material comprising root crop which is moved along relative to a machine frame by means of at least one conveyor element. A conveying speed of the conveyor element is set on the basis of a test data set which is generated using the test image or formed by means of the latter. An evaluation device generates, on the basis of the test data set, a conveying speed signal, independent of a speed of the harvested material, for setting the conveying speed.