ViewController.swift

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var imageView: UIImageView!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }

    @IBAction func didTapButton(_ sender: Any) {
        let picker = UIImagePickerController()

//        picker.sourceType = .camera
        picker.sourceType = .photoLibrary

        picker.delegate = self
        present(picker, animated: true)
    }

}

extension ViewController: UIImagePickerControllerDelegate, UINavigationControllerDelegate {
    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {

        imageView.image = info[.originalImage] as? UIImage
        dismiss(animated: true)
    }
}