How do I crop an image in Flutter?

I would probably use a BoxDecoration with a DecorationImage. You can use the alignment and fit properties to determine how your image is cropped. You can use an AspectRatio widget if you don't want to hard code a height on the Container.

import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(
    home: new MyHomePage(),
  ));
}

class MyHomePage extends StatelessWidget {

  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text("Image Crop Example"),
      ),
      body: new Center(
        child: new AspectRatio(
          aspectRatio: 487 / 451,
          child: new Container(
            decoration: new BoxDecoration(
              image: new DecorationImage(
                fit: BoxFit.fitWidth,
                alignment: FractionalOffset.topCenter,
                image: new NetworkImage('https://i.stack.imgur.com/lkd0a.png'),
              )
            ),
          ),
        ),
      ),
    );
  }
}

Take a look to brendan-duncan/image, it's platform-independent library to manipulate images in Dart.

You can use the function:

Image copyCrop(Image src, int x, int y, int w, int h);

Provide a fit factor to your Image widget and then wrap it in AspectRatio.

AspectRatio(
  aspectRatio: 1.5, 
  child: Image.asset(
    'your_image_asset',
    fit: BoxFit.cover,
  ),
)

You can also directly use the Image class with BoxFit and do something like:

new Image.asset(
  stringToImageLocation,
  fit: BoxFit.cover,
)