Scanners.

[riju]

• Barcode / QR code scanning
  { ZBar / Zxing } needed ?

• Document Scanner - Page/Book/ ID / receipts
  {edge_detection -> find contour -> four_point_transform }

• CreditCard Scanner
  simple OCR {alpha numeric} no need to manually enter CC details.

• OCR / Text Recognition
  { tesseract has a JavaScript fork}

The Shape Detection API can be a good reference point as we are trying out similar things using OpencvJS+WASM.