The Image Viewer addon has more useful features to offer — Random Image and Initial Frame, which give users a chance to choose the addon’s preview image.
In order to set the “Random Image” option, simply tick the relevant checkbox in the Properties side menu, and the preview image will be chosen randomly. If you wish to set a specific frame as a preview image, simply enter its number in the “Initial frame” box.
An updated documentation of the Image Viewer addon is available here. If you wish to view a demo presentation, click here.