Solution for this topic

To have a background per category you have to develop and use custom CSS code like following by adding it in the Custom CSS code option of your theme on the below path.

Admin Area -> Appearance -> Theme Settings -> Custom Code -> CSS Code

.tax-product_cat.term-test-album-scooby-category .sh-titlebar {
    background-image: url(//www.worldofpixels.be/wp-content/uploads/2016/03/pexels-photo-v270221.jpeg);
}

To create the CSS code for other categories just copy paste the above CSS code and change the category name and background image URL in it.