An image can be added to the widget header to make your design more visually appealing. You can add an image by going to Design > Themes and click on the theme that you intend on editing.
Once you are in the theme, click on the Sections tab on the left side of the window next to the General Settings tab. Find and click on the widget that you want to edit from the Sections tab and the widget Edit Content window will appear.
Tick the 'Customise This Widget' box under Widget Design and then tick the Header BG Image box. You can now upload a header image and customise the widget header settings.
Finally, click 'Apply and Close' at bottom of Widget Edit Content to apply changes to the widget and click Save Theme Settings to save widget changes to that theme.