A data processing apparatus is arranged to receive successive images from a video camera. The apparatus includes means for detecting inter-image motion for selected points in an image region associated with a control function of the apparatus. The apparatus also includes means for executing the control function if inter-image motion is detected in the image region. The detecting means is configured to select points in an image region of a current image that are validated by selecting test points in a currently received image based upon their correspondence with points in a preceding received image. The points in the preceding received image themselves corresponding with the points originally selected in the currently received image. The detecting means is also configured to deselect points in the current image whose corresponding test points do not substantially coincide therewith.