The present invention relates to a registration system for labels in labelling machines, in order to provide the correct positioning of a label on an object, namely on a container. The registration system for the label adjustment in a labelling unit comprises optical sensing means (6), encoding means (7) and a computing and control system, and provides for a first stage of setting, in order to identify in the label a reference region, and a second stage of processing comprising reading the position of a processing region of the labels in a label film (3) corresponding to the said reference region and controlling an operation of the labelling unit as a function of the position read for the said processing region, and it provides for the following steps : reading one or more test labels in the label film (3), preferably the heading one or more labels of the said film (3); selecting part of or the whole region of the printed matter of said one or more test label as a reference region that functions as a virtual mark of the label, wherein the said selection is made on the basis of the maximization of the signal-to-noise ratio or of a contrast measure; reading a subsequent processing label; - Computing the length of the processing label under examination as the distance between a processing region and the reference region of the one or more test labels.