BuddyPress.org

Within the profile when logged in the user can select and add their own cover image. This will allow all users to have their own unique cover images.

You might want to make sure your images are not too big and the correct proportions otherwise they will be cropped. Depending on your theme this size might vary but a good starting point would be 1350px wide and 350px tall or for full screen width 1920px x 640px.

Hi Paul

You can try this code to set one background image for all users.
Please change the image URL to point at your image.

function set_default_cover_image( $settings = array() ) {
    $settings['default_cover'] = 'your-image-url.jpg';
 
    return $settings;
}
add_filter( 'bp_before_members_cover_image_settings_parse_args', 'set_default_cover_image', 10, 1 );