Follow the following steps:

1. Create the folders called assets/images inside project but outside lib folder.
2. Now Open pubspec.yaml and add:

(The indents must be precise)

3. After updating pubspec.yaml close the app and RUN IT AGAIN.
4. Now your code will work: (All possible ways)

Container(
  height: 200, //As per your requirement
  width: 200,//As per your requirement
  child: Image(
    image: AssetImage(
      'assets/images/profile.png',
    ),
    fit: BoxFit.cover,
  )
)

Container(
  height: 200, //As per your requirement
  width: 200,//As per your requirement
  decoration: BoxDecoration(
    image: DecorationImage(
      'assets/images/profile.png',
      fit: BoxFit.cover,
    )
  )
)

Container(
  height: 200, //As per your requirement
  width: 200,//As per your requirement
  child: Image.asset(
    'assets/images/profile.png',
    fit: BoxFit.cover,
  )
)