Given that PlayFilm enables to link different video clips randomly or after a user’s action, the empty spaces on Timeline are never shown during the playback of the project. Therefore, the only way to show a static image in an interactive video, is by adding an Empty vídeo to Timeline and assign a poster to it. By that means, when the empty video is shown, it will actually play the poster image during the given time of the Empty video.
To do so, select the empty video in Timeline and go to its Properties Tab. In the General submenu, you will find available the Poster option, select an image from the dropdown menu and you just have assigned a poster to your empty video.