clip_oval.dart

class _MyHomePageState extends State<MyHomePage> {
  String imageSource =
      'https://images.unsplash.com/photo-1492633423870-43d1cd2775eb?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=1350&q=80';


  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      backgroundColor: Colors.blueGrey,
      body: Center(
        child: ClipOval(   // <- Where the magic happens
          child: Image.network(
            imageSource,
            width: 300,
            height: 300,
            fit: BoxFit.cover,
          ),
        ),
      ),
    );
  }
}