ImageButton.swift

import UIKit

class ImageButton: UIButton {

    override init(frame: CGRect) {

        super.init(frame: frame)
    }

    required init?(coder aDecoder: NSCoder) {

        super.init(coder: aDecoder)
    }

    override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {

        if self.imageView?.image?.getAlpha(point) == 0 {

            return nil
        } else {

            return super.hitTest(point, with: event)
        }
    }
}

extension UIImage {

    func getAlpha(_ pos: CGPoint) -> CGFloat {

        let imageData = self.cgImage?.dataProvider?.data!
        let data: UnsafePointer = CFDataGetBytePtr(imageData)

        let address: Int = ((Int(self.size.width) * Int(pos.y)) + Int(pos.x)) * 4

        return CGFloat(data[address + 3])
    }
}