Lead Developer
You can place whatever you like in the sidebars. Simply go to “Appearance > Widgets” and drag your desired widget into a widget area.
You can use the “Text” widget to add your image HTML, or you can use a plugin like this to upload an image directly to the widget: https://wordpress.org/plugins/image-widget/
Documentation: http://docs.generatepress.com/
Adding CSS: http://docs.generatepress.com/article/adding-css/
Ongoing Development: https://generatepress.com/ongoing-development