Hello,

Sorry for the late reply!
To add an image for your footer background, you need to use custom css. Add the code into your custom css box in General Options. An example code is this:

footer#footer .inner {
  background-image: url("https://codeless.co/specular/default/wp-content/uploads/2014/07/1231-compressed.jpg");
  background-size: cover;
  background-position: center center;
}

Change the link of the image to your wish.

Best regards!