The image viewer has a plugin system which uses the Python scripting language. If you activate the Python console, you can gain direct access to a Python interpreter from inside the image viewer, which you can then use to write scripts or programmatically manipulate images, for example.
In order to enable this feature, you need to have installed.
Once eog-plugins is installed, press the menu button in the top-right corner of the window, select Preferences, and go to the Plugins tab.
Check Python Console and click Close.
Click the Python Console menu item to bring up the console.