Background Image for Scaffold

Setting the backgroundColor:Colors.transparent is the key you are missing.

You can place your Scaffold inside Container with background image and use transparent color for Scaffold's body like this:

Container(
  decoration: BoxDecoration(
    image: DecorationImage(
      image: AssetImage("assets/bg.jpg"),
      fit: BoxFit.cover,
    ),
  ),
  child: Scaffold(
    appBar: AppBar(
      title: Text(widget.title),
    ),
    backgroundColor: Colors.transparent,
    body: Container(),
),);

Try using Stack check the following sample:

  @override
    Widget build(BuildContext context) {
      return Stack(
        children: <Widget>[
          Image.asset(
            "resources/background.png",
            height: MediaQuery.of(context).size.height,
            width: MediaQuery.of(context).size.width,
            fit: BoxFit.cover,
          ),
          Scaffold(
              backgroundColor: Colors.transparent,
              appBar: AppBar(
                backgroundColor: Colors.transparent,
                elevation: 0.0,
              ),
              bottomNavigationBar: Container(
                padding: EdgeInsets.only(left: 4.0, right: 4.0),
                height: 44.0 + MediaQuery.of(context).padding.bottom,
                child: Row(
                  mainAxisAlignment: MainAxisAlignment.spaceBetween,
                  children: <Widget>[
                    IconButton(icon: Icon(Icons.star)),
                    IconButton(icon: Icon(Icons.star)),
                  ],
                ),
              ),
              body: Text("Hello world"))
        ],
      );
    }