When you click on “Edit Sidebar” you should see a section called “Sidebar Background”. There you have controls for uploading a background image and some settings as to how it will display. Here’s a screenshot of how that looks like:
For Bootstrap media objects you will need the Bootstrap Shortcodes for WordPress plugin. This tutorial explains how to use the plugin and in this page you can see a working example of a media object along with how the shortcode was written.