For luggage inspection, a good 3D impression is needed. This impression can be enhanced either by improving the image quality or by providing multiple viewpoints. An experiment is described in which students had to judge whether two objects in a transparent box were connected with a wire. Subjects using head movements to select the viewpoint were compared with subjects using a knob. Viewpoint selection was limited to horizontal movement. The resolution and the number of grey levels of the image as well as the size and the number of discrete steps of image movement were manipulated. Results show that 16 grey levels are sufficient to detect the wire, but that for a correct decision about connectivity, a freedom of movement of at least 90° is desirable. No difference was found between selecting the desired viewpoint with the head and by knob.