override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch = touches.first as UITouch?{
            let touchPoint = touch.location(in: self.lassoImageView) + lassoOffset!
            print("touch begin to : (touchPoint)")
            eraserStartPoint = touchPoint
        }
    }

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch = touches.first as UITouch?{
            let touchPoint = touch.location(in: self.lassoImageView) + lassoOffset!
            print("touch moved to : (touchPoint)")
            erase(fromPoint: eraserStartPoint!, toPoint: touchPoint)
            eraserStartPoint = touchPoint
        }
    }

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch = touches.first as UITouch?{
            let touchPoint = touch.location(in: self.lassoImageView) + lassoOffset!
            print("touch ended at : (touchPoint)")
            erase(fromPoint: touchPoint, toPoint: touchPoint)
            UIGraphicsBeginImageContext(lassoImageView.frame.size)
                lassoImageView.image?.draw(in: CGRect(x: 0, y: 0, width: lassoImageView.frame.size.width, height: lassoImageView.frame.size.height), blendMode: .normal, alpha: 1.0)
                lassoImageView.image?.draw(in:  CGRect(x: 0, y: 0, width: lassoImageView.frame.size.width, height: lassoImageView.frame.size.height), blendMode: .normal, alpha: 1.0)
                lassoImageView.image = UIGraphicsGetImageFromCurrentImageContext()
                UIGraphicsEndImageContext()
    }

func erase(fromPoint: CGPoint, toPoint: CGPoint) {
        UIGraphicsBeginImageContextWithOptions(lassoImageView.bounds.size, false, 1)
        //UIGraphicsBeginImageContext(lassoImageView.bounds.size)
        //UIGraphicsBeginImageContext(lassoImageView.image!.size)
        let context = UIGraphicsGetCurrentContext()
        lassoImageView.image?.draw(in: CGRect(x: 0, y: 0, width: lassoImageView.frame.size.width, height: lassoImageView.frame.size.height))
        //lassoImageView.image?.draw(in: calculateRectOfImageInImageView(imageView: lassoImageView))

        context?.move(to: fromPoint)
        context?.addLine(to: toPoint)

        context?.setLineCap(.round)
        context?.setLineWidth(CGFloat(eraserBrushWidth))

        context?.setBlendMode(.clear)

        context?.strokePath()

        lassoImageView.image = UIGraphicsGetImageFromCurrentImageContext()
        croppedImage = UIGraphicsGetImageFromCurrentImageContext()

        UIGraphicsEndImageContext()
    }

lassoImageView // this is UIImageView where I'm loading image from gallery and then erasing image with my finger

lassoOffset // this is Float for touch offset because finger hides part of image

lassoImageView.image?.draw(in: CGRect(x: 0, y: 0, width: lassoImageView.frame.size.width, height: lassoImageView.frame.size.height))