A method for closed-loop controlling a processing operation of a workpiece, comprising the steps of: (a) recording a pixel image at an initial time point of an interaction zone by means of a camera, wherein the workpiece is processed using an actuator having an initial actuator value, wherein the position and orientation of the keyhole in the recorded pixel image is normalized according to a method for classifying a multitude of images recorded by a camera observing a processing area of a workpiece processed by a processing beam, comprising the steps of: - recording a first pixel image and a multitude of subsequent pixel images by the camera during a processing operation; - detecting mismatches of a position and orientation of a keyhole generated by the processing beam in the workpiece within an image plane of the subsequent pixel images in comparison to the first pixel image; - compensating the mismatches of the position and orientation of the respective keyholes in the subsequent pixel images with regard to the first pixel image, to produce a set of pixel images having each a normalized keyhole position and orientation; - classifying the set of normalized pixel images into at least two classes by means of a classifier; (b) converting the pixel image into a pixel vector; (c) representing the pixel vector by a sum of predetermined pixel mappings each multiplied by a corresponding feature value; (d) classifying the set of feature values on the basis of learned feature values into at least two classes of a group of classes comprising a first class of a too high actuator value, a second class of a sufficient actuator value and a third class of a too low actuator value at the initial time point; (e) performing a control step for adapting the actuator value by minimizing the error e t, between a quality indicator y e and a desired value; and (f) repeating the steps (a) to (e) for further time points to perform a closed-loop controlled processing operation. (a) recording a pixel image at an initial time point of an interaction zone by means of a camera, wherein the workpiece is processed using an actuator having an initial actuator value, wherein the position and orientation of the keyhole in the recorded pixel image is normalized according to a method for classifying a multitude of images recorded by a camera observing a processing area of a workpiece processed by a processing beam, comprising the steps of: - recording a first pixel image and a multitude of subsequent pixel images by the camera during a processing operation; - detecting mismatches of a position and orientation of a keyhole generated by the processing beam in the workpiece within an image plane of the subsequent pixel images in comparison to the first pixel image; - compensating the mismatches of the position and orientation of the respective keyholes in the subsequent pixel images with regard to the first pixel image, to produce a set of pixel images having each a normalized keyhole position and orientation; - classifying the set of normalized pixel images into at least two classes by means of a classifier; - recording a first pixel image and a multitude of subsequent pixel images by the camera during a processing operation; - detecting mismatches of a position and orientation of a keyhole generated by the processing beam in the workpiece within an image plane of the subsequent pixel images in comparison to the first pixel image; - compensating the mismatches of the position and orientation of the respective keyholes in the subsequent pixel images with regard to the first pixel image, to produce a set of pixel images having each a normalized keyhole position and orientation; - classifying the set of normalized pixel images into at least two classes by means of a classifier; (b) converting the pixel image into a pixel vector; (c) representing the pixel vector by a sum of predetermined pixel mappings each multiplied by a corresponding feature value; (d) classifying the set of feature values on the basis of learned feature values into at least two classes of a group of classes comprising a first class of a too high actuator value, a second class of a sufficient actuator value and a third class of a too low actuator value at the initial time point; (e) performing a control step for adapting the actuator value by minimizing the error e t, between a quality indicator y e and a desired value; and (f) repeating the steps (a) to (e) for further time points to perform a closed-loop controlled processing operation.