If you are running Une Boutique 2.0+ you now have another premium plugin named Ultimate Add-on for Visual Composer which added many more functionalities to Visual Composer, among which there are new options for row backgrounds, since this plugin overrides the default row backgrounds, the new options can now be found in the bottom of Edit Row pop-up.
Scroll down to the bottom of the Edit Row pop-up and from the Background Style drop down select image. If you are not planing to have a parallax style background, set it’s option to Simple Background Image, select your background image set the repeating, sizing etc. options and save everything.
If you are not planing to use the Ultimate Addons for Visual Composer plugin, you can still add background images to your row, with the difference that the option is almost at the top of the edit row pop-up and you do not have an option to make the background parallax effect.
In this case below the background color and font color option on your Edit Row pop-up you can find the option where you can assign your background image to the row.