Painting over image

paiting_image.dart

import 'package:flutter/material.dart';

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: MyWidget(),
        ),
      ),
    );
  }
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(
    child: CustomPaint(
      foregroundPainter: MyPainter(),
    child: Image.network("https://www.alfabetajuega.com/wp-content/uploads/2019/11/dragon-ball-goku-aura-770x436.jpg", fit: BoxFit.cover),
    ),);
  }
}

class MyPainter extends CustomPainter {
    
  void paint(Canvas canvas, Size size){
    canvas.drawCircle(Offset(size.width/2, size.height/2), size.width/4, Paint());
  }
  
  bool shouldRepaint (MyPainter old) => true;
  
}