Flutter Camera Overlay

You can also now use this plugin : CamerAwesome

Official plugin has a ratio bug that makes overlay having bad ratio. This plugin includes flash, zoom, auto focus... and no initialisation required.

Please visit this repo. This example uses the camera plugin.

new AspectRatio(
  aspectRatio: controller.value.aspectRatio,
  child: Container(
    child: Stack(
      children: <Widget>[
        CameraPreview(controller),
        Align(
          alignment: Alignment.bottomCenter,
          child: Container(
            width: double.infinity,
            height: 120.0,
            padding: EdgeInsets.all(20.0),
            color: Color.fromRGBO(00, 00, 00, 0.7),
            child: Stack(
              children: <Widget>[
                Align(
                  alignment: Alignment.center,
                  child: Material(
                    color: Colors.transparent,
                    child: InkWell(
                      borderRadius: BorderRadius.all(Radius.circular(50.0)),
                      onTap: () {
                        _captureImage();
                      },
                      child: Container(
                        padding: EdgeInsets.all(4.0),
                        child: Image.asset(
                          'assets/images/ic_shutter_1.png',
                          width: 72.0,
                          height: 72.0,
                        ),
                      ),
                    ),
                  ),
                ),
                Align(
                  alignment: Alignment.centerRight,
                  child: Material(
                    color: Colors.transparent,
                    child: InkWell(
                      borderRadius: BorderRadius.all(Radius.circular(50.0)),
                      onTap: () {
                        if (!_toggleCamera) {
                          onCameraSelected(widget.cameras[1]);
                          setState(() {
                            _toggleCamera = true;
                          });
                        } else {
                          onCameraSelected(widget.cameras[0]);
                          setState(() {
                            _toggleCamera = false;
                          });
                        }
                      },
                      child: Container(
                        padding: EdgeInsets.all(4.0),
                        child: Image.asset(
                          'assets/images/ic_switch_camera_3.png',
                          color: Colors.grey[200],
                          width: 42.0,
                          height: 42.0,
                        ),
                      ),
                    ),
                  ),
                ),
              ],
            ),
          ),
        ),
      ],
    ),
  ),
);

.

You can use the camera Plugin for flutter by the Flutter team.

https://pub.dartlang.org/packages/camera

and then position your image and you cameraview in a Stack Widget like this:

return new Stack(
  alignment: FractionalOffset.center,
  children: <Widget>[
    new Positioned.fill(
      child: new AspectRatio(
          aspectRatio: controller.value.aspectRatio,
          child: new CameraPreview(controller)),
    ),
    new Positioned.fill(
      child: new Opacity(
        opacity: 0.3,
        child: new Image.network(
          'https://picsum.photos/3000/4000',
          fit: BoxFit.fill,
        ),
      ),
    ),
  ],
);