Put picture for background

Somebody please tell me how I are put picture for background inside me meeting. I know I are use interface_config.js DEFAULT_BACKGROUND are change color but I want put picture instede color. Please sugeste me how to do?

Try config.js

    /**
     External API url used to receive branding specific information.
     If there is no url set or there are missing fields, the defaults are applied.
     The config file should be in JSON.
     None of the fields are mandatory and the response must have the shape:
     {
         // The domain url to apply (will replace the domain in the sharing conference link/embed section)
         inviteDomain: 'example-company.org,
         // The hex value for the colour used as background
         backgroundColor: '#fff',
         // The url for the image used as background
         backgroundImageUrl: 'https://example.com/background-img.png',
         // The anchor url used when clicking the logo image
         logoClickUrl: 'https://example-company.org',
         // The url used for the image used as logo
         logoImageUrl: 'https://example.com/logo-img.png',
         // Overwrite for pool of background images for avatars
         avatarBackgrounds: ['url(https://example.com/avatar-background-1.png)', '#FFF'],
         // The lobby/prejoin screen background
         premeetingBackground: 'url(https://example.com/premeeting-background.png)'
     }
    */

@Jose_Luis_Andrade thank you for me responde. I try this but he are no work for me what I do wronge?