Abstract: A video image of a relatively simple nature is produced by scanning using a conventional TV camera (1), and the scan results are converted into a Cartesian co-ordinate form for image analysis. This involves seeking a point of interest during the scan, the number of scan steps along a scan line as indicated by a counter (11) defining the point's location along the line. The point of interest's location in the other co-ordinate is indicated by the setting of a scan line counter (6). After each detection of a point of interest its location is indicated to associated equipment and the scan is resumed. As described this is used in an eye follower of the type described in our U.S. Pat. No. 1,581,018 the image analysis being used to assess the directions in which the eye is looking. The result of this assessment is used to exercise a controlling function or a machine or other device, e.g. to enable a disabled person to control such a machine or device.