Alright, let's get started! First things first, you need to set up Firebase in your Android or iOS app where you want to add the barcode scanning feature. This means creating a Firebase project in the Firebase console, registering your app, and adding the Firebase SDK to your app.

Once you've got Firebase all set up, it's time to add the Firebase ML Vision dependency. For Android, just pop these lines into your app-level build.gradle file:

implementation 'com.google.firebase:firebase-ml-vision:24.1.0'

For iOS, you'll need to add this line to your Podfile:

pod 'Firebase/MLVisionBarcodeModel'

Then, run the pod install command. Easy peasy, right?

Now, let's talk about the image. Barcode scanning needs an image as input. This image can come from different sources: live camera feed, static image files, or even a byte buffer. You need to wrap this image in an InputImage object and pass it to the Barcode Scanning API. Here's how you do it for images from a camera feed or media files:

// For Android
InputImage image;
image = InputImage.fromBitmap(bitmap, rotationDegree);

// For iOS
let image = VisionImage(image: uiImage)

Next up, you need to initialize the barcode detector. For Android, use the FirebaseVision class to get an instance of FirebaseVisionBarcodeDetector. For iOS, use the Vision class for the same.

// Android
FirebaseVisionBarcodeDetectorOptions options =
  new FirebaseVisionBarcodeDetectorOptions.Builder()
    .setBarcodeFormats(
      FirebaseVisionBarcode.FORMAT_QR_CODE,
      FirebaseVisionBarcode.FORMAT_AZTEC)
    .build();

FirebaseVisionBarcodeDetector detector = FirebaseVision
  .getInstance()
  .getVisionBarcodeDetector(options);

// iOS
let barcodeFormat = VisionBarcodeFormat.qrCode
let options = VisionBarcodeDetectorOptions(formats: barcodeFormat)

lazy var vision = Vision.vision()
let barcodeDetector = vision.barcodeDetector(options: options)

Now, let's process that image using the barcode detector's detect method. This is done asynchronously, so be ready to handle errors and results in the provided callbacks.

// Android
Task<List<FirebaseVisionBarcode>> result = 
  detector.detectInImage(image)
    .addOnSuccessListener(new OnSuccessListener<List<FirebaseVisionBarcode>>() {
      @Override
      public void onSuccess(List<FirebaseVisionBarcode> barcodes) {
        // Task completed successfully
        // ...
      }
    })
    .addOnFailureListener(new OnFailureListener() {
      @Override
      public void onFailure(@NonNull Exception e) {
        // Task failed with an exception
        // ...
      }
    });

// iOS
barcodeDetector.detect(in: visionImage) { features, error in
  guard error == nil, let features = features, !features.isEmpty else {
    // Error handling
    return 
  }
  
  for feature in features {
    // Handle detected features
  }
}

Finally, you get a list of detected barcodes in the success listener. Each detected barcode contains different pieces of information depending on the barcode's contents and format.

// For Android
for (FirebaseVisionBarcode barcode: barcodes) {
  Rect bounds = barcode.getBoundingBox();
  Point[] corners = barcode.getCornerPoints();

  String rawValue = barcode.getRawValue();
  int valueType = barcode.getValueType();

  // See API documentation for more information about possible types
}

// For iOS
for barcode in features {
  let corners = barcode.cornerPoints
  let displayValue = barcode.displayValue
  let rawValue = barcode.rawValue
  
  // See Firebase documentation for more information about possible types
}

After you've processed the images and got the results you need, don't forget to release the detector using detector.close() (for Android) or barcodeDetector = nil (for iOS) to free up the resources.