A method comprising: displaying a user interface on a display of a user terminal for display of received video frames; detecting selection of a selectable button displayed in said user interface by a user using an input device of said user terminal whilst a first received video frame is displayed in the user interface; in response to said detection, disabling the display of video frames received after said first received video frame; determining a position of a face of a user in the first received video frame by executing a face tracker algorithm on a processor of said user terminal; receiving image data to be applied at a facial position on said face; modifying the first received video frame by applying the image data to each of said facial positions on the face; detecting a condition and in response to detecting said condition, for a plurality of further video frames received after detecting said condition: determining a position of the face in each of the further video frames by executing the face tracker algorithm to determine the location of the plurality of facial positions in each of the further video frames, modifying each of the further video frames by applying the image data to each of said facial positions on the face; and displaying each of the modified further video frames in the user interface, characterized in that the method is implemented at the user terminal during a video call conducted with at least one further user terminal over a communications network; the method further comprises receiving a plurality of drawing inputs (801a, 801b) whilst the selectable button is in a selected state, each drawing input (801a, 801b) defining said image data to be applied at said facial position on said face; and wherein the modified further video frames are displayed in the user interface such that the displayed modified further video frame for each further video frame received after detecting said condition comprises image data which is mapped onto points, corresponding to said facial positions, of the face of the user identified by the face tracker algorithm so that the drawing input (801a, 801b) moves with the face of the user in three dimensions when displayed as a video call. displaying a user interface on a display of a user terminal for display of received video frames; detecting selection of a selectable button displayed in said user interface by a user using an input device of said user terminal whilst a first received video frame is displayed in the user interface; in response to said detection, disabling the display of video frames received after said first received video frame; determining a position of a face of a user in the first received video frame by executing a face tracker algorithm on a processor of said user terminal; receiving image data to be applied at a facial position on said face; modifying the first received video frame by applying the image data to each of said facial positions on the face; detecting a condition and in response to detecting said condition, for a plurality of further video frames received after detecting said condition: determining a position of the face in each of the further video frames by executing the face tracker algorithm to determine the location of the plurality of facial positions in each of the further video frames, modifying each of the further video frames by applying the image data to each of said facial positions on the face; and displaying each of the modified further video frames in the user interface, determining a position of the face in each of the further video frames by executing the face tracker algorithm to determine the location of the plurality of facial positions in each of the further video frames, modifying each of the further video frames by applying the image data to each of said facial positions on the face; and displaying each of the modified further video frames in the user interface, characterized in that the method is implemented at the user terminal during a video call conducted with at least one further user terminal over a communications network; the method further comprises receiving a plurality of drawing inputs (801a, 801b) whilst the selectable button is in a selected state, each drawing input (801a, 801b) defining said image data to be applied at said facial position on said face; and wherein the modified further video frames are displayed in the user interface such that the displayed modified further video frame for each further video frame received after detecting said condition comprises image data which is mapped onto points, corresponding to said facial positions, of the face of the user identified by the face tracker algorithm so that the drawing input (801a, 801b) moves with the face of the user in three dimensions when displayed as a video call.