Check out example codes for "how to add image from assets inside as a decoration image in container". It will help you in understanding the concepts better.

Code Example 1

Container(
      height: 120.0,
      width: 120.0,
      decoration: BoxDecoration(
        image: DecorationImage(
          image: AssetImage(
              'assets/assets/alucard.jpg'),
          fit: BoxFit.fill,
        ),
        shape: BoxShape.circle,
      ),
    )

Code Example 2

new Container(
  width: 100.00,
  height: 100.00,
  decoration: new BoxDecoration(
  image: new DecorationImage(
      image: ExactAssetImage('assets/example.png'),
      fit: BoxFit.fitHeight,
      ),
  ));

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