Getting image part of VNTextObservation rectangles in Vision Framework

Question

I am able to get the rectangles of text detected in vision framework video feed in iOS 11, but I am trying to get the image part of video that was recognized as a text or character. Someone can help in that?

 func detectTextHandler(request: VNRequest, error: Error?) {
    guard let observations = request.results else {
        print("no result")
        return
    }

    let result = observations.map({$0 as? VNTextObservation})

    DispatchQueue.main.async() {
        self.imageView.layer.sublayers?.removeSubrange(1...)
        for region in result {
            guard let rg = region else {
                continue
            }

            self.highlightWord(box: rg)

            if let boxes = region?.characterBoxes {
                for characterBox in boxes {
                    self.highlightLetters(box: characterBox)
                }
            }
        }
    }
}

So how can I get the image part of region?.characterBoxes