Upload the image to the Library of your Ubertor control panel.
1. Log in to your site's Control Panel.
2. Click on Library tab on left menu bar
3. Click 'Upload New Media' on top right
4. Select file or drop file from your computer
The URL to the specific image will never change. You are able to edit the image in your Library, but the source URL for that specific image will remain the same, not causing issues with your CSS implementation.