Images are printed on surfaces of discrete objects that are loaded onto an upstream end of a production path passing through a plurality of treatment stations and taken off a downstream end the path. The path passes through a plurality of treatment stations and is split at least one of the stations into a plurality of generally parallel lanes each having a respective treatment device or printer. At the one treatment station the objects are split up and fed to the lanes from the path, the images are printed on the objects in the lanes with the respective printers, and all the objects are returned to the path after printing. The objects move single-file downstream along the path upstream and downstream of the one station. Instead of printers, each lane can have some other type of treatment machine and the operations performed by these treatment machines in the lanes can be the same or different.