This reply has been accepted as the best answer.
try with this public URL using the rule below in the footer widget area CSS+ box
{background:url(https://www.aaronreedphotography.com/images/xl/The-Wash-Web-2019.jpg);background-size:contain;}
OR with the rule below in the theme Global Custom CSS
#footer-widget-area {background:url(https://www.aaronreedphotography.com/images/xl/The-Wash-Web-2019.jpg);background-size:contain;}
And if that does not work, post the link to your site , letting me know in which CSS box you placed which rule