A visual detection arrangement is provided in a milking system (3) comprising a robot arm (15) for attaching a teat cup (11) to a teat of a milking animal (8), and a control device (19) for controlling the movement of the robot arm. The detection arrangement comprises first visual detection means (17) provided on the robot arm for repeatedly determining the teat position relative the robot arm and second visual detection means (21) directed towards the milking animal. The second visual detection means (21) is provided for detecting a position of the animal in a longitudinal direction (x), and the control device (19) is initially provided for controlling the movement of the robot arm based on information of the position of the teat of the animal relative the animal itself, and on the detected longitudinal position of the animal.