This feature have the purpose to access graphically the functionalities of plugins added in eog. By default, the box is hidden to avoid a change in the behaviour of Eog and can be display via the show submenu. It will be possible to insert plugins inside the box with the method eog_window_get_boxtool and in the menu.
I'm working for Ordissimo who sold laptop with a derivative of debian on it to 100,000 seniors and we intend to add Eog as the official image viewer for his simplicity (see our our website for more information)