A labelling machine for liquid containers, each of the containers being elongate along a respective longitudinal axis and having a seam lying in a seam plane containing the longitudinal axis, wherein the machine comprises: - a carousel which rotates about a central axis of rotation; - a plurality of supporting elements, rotating about respective supporting axes and configured to support respective containers in rotation about the respective supporting axes which operatively coincide with the longitudinal axes of the respective containers, the supporting elements being integral with the carousel to transport the containers along a predetermined path in rotation about the central axis; - a plurality of actuators mounted on the carousel and connected to respective supporting elements to move them about the respective supporting axes; - an optical inspection device, having an illuminator to light at least one sector of the path, at least one camera to capture one or more images of the containers supported by the supporting elements and positioned in the sector, and a processing unit configured to process the images in order to identify the position of the respective seams on the containers, wherein the illuminator of the optical inspection device is arranged in a stationary position with respect to the carousel and comprises a light generator defining a light emitting surface; wherein said at least one camera is positioned by the same side of the illuminator as compared to the illuminated containers, wherein the illuminator comprises a collimator, interposed between the light generator and the carousel, defining a lighting surface which faces towards the sector of the path, and configured, in the context of the light rays generated by the light generator and incident upon the collimator, to block the rays whose inclination is greater than a critical angle relative to corresponding planes which are parallel to the supporting axes and at right angles to the collimator at the respective points of incidence of the incident light rays, wherein the collimator includes a layer having a first face and a second face (3b") opposite the first face, the first face of the collimator being directed towards the illuminator, to define a surface of incidence for the light rays generated by the illuminator, the second face (3b") of the collimator being directed towards the carousel to define the lighting surface, wherein the illuminator is configured to generate a uniform light field directed outwards from the lighting surface, characterized in that the illuminator comprises a diffuser interposed between the light generator and the collimator and which defines a first surface directed towards the emitting surface, and a second surface (3d") directed towards the lighting surface, in order to diffuse the light rays coming from the light generator and directed towards the collimator. - a carousel which rotates about a central axis of rotation; - a plurality of supporting elements, rotating about respective supporting axes and configured to support respective containers in rotation about the respective supporting axes which operatively coincide with the longitudinal axes of the respective containers, the supporting elements being integral with the carousel to transport the containers along a predetermined path in rotation about the central axis; - a plurality of actuators mounted on the carousel and connected to respective supporting elements to move them about the respective supporting axes; - an optical inspection device, having an illuminator to light at least one sector of the path, at least one camera to capture one or more images of the containers supported by the supporting elements and positioned in the sector, and a processing unit configured to process the images in order to identify the position of the respective seams on the containers, wherein the illuminator of the optical inspection device is arranged in a stationary position with respect to the carousel and comprises a light generator defining a light emitting surface; wherein said at least one camera is positioned by the same side of the illuminator as compared to the illuminated containers, wherein the illuminator comprises a collimator, interposed between the light generator and the carousel, defining a lighting surface which faces towards the sector of the path, and configured, in the context of the light rays generated by the light generator and incident upon the collimator, to block the rays whose inclination is greater than a critical angle relative to corresponding planes which are parallel to the supporting axes and at right angles to the collimator at the respective points of incidence of the incident light rays, wherein the collimator includes a layer having a first face and a second face (3b") opposite the first face, the first face of the collimator being directed towards the illuminator, to define a surface of incidence for the light rays generated by the illuminator, the second face (3b") of the collimator being directed towards the carousel to define the lighting surface, wherein the illuminator is configured to generate a uniform light field directed outwards from the lighting surface, characterized in that the illuminator comprises a diffuser interposed between the light generator and the collimator and which defines a first surface directed towards the emitting surface, and a second surface (3d") directed towards the lighting surface, in order to diffuse the light rays coming from the light generator and directed towards the collimator.