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If you want to use an image from your iOS device, you'll want to use this. First put Privacy - Photo Library Usage Description with a string description into your Info.plist file.

Next define let picker = UIImagePickerController() and in your viewDidLoad() set its delegate as picker.delegate = self.

You can start it using:

  picker.allowsEditing = false
  picker.sourceType = .photoLibrary
  self.present(picker, animated: true, completion: nil)

Since we've made our class the delegate, you need to make the class use these protocols: UIImagePickerControllerDelegate, UINavigationControllerDelegate.

And we define two methods, one that dismisses the popup and another that grabs our image:

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
    let chosenImage = info[UIImagePickerControllerOriginalImage] as! UIImage
    // use the image
    dismiss(animated: true, completion: nil)
}

func imagePickerControllerDidCancel(_ picker: UIImagePickerController) {
    dismiss(animated: true, completion: nil)
}

If you want to use the camera instead of the photo album, change your initialisation code to:

picker.allowsEditing = false
picker.sourceType = .camera
picker.cameraCaptureMode = .photo