My below code was working just fine with swift 4 but after upgrading to swift 4.2 I am getting this error, I had wasted my 3 hours searching what's the issue but failed. Please if anyone can guide me how to fix this.
func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
    if postType == 2 {
        let image = info[convertFromUIImagePickerControllerInfoKey(UIImagePickerController.InfoKey)] as! UIImage
        mediaType.image = image
    } else {
        videoURL = info[convertFromUIImagePickerControllerInfoKey(UIImagePickerController.InfoKey.mediaURL)] as? URL
        do {
            let asset = AVURLAsset(url: videoURL!, options: nil)
            let imgGenerator = AVAssetImageGenerator(asset: asset)
            imgGenerator.appliesPreferredTrackTransform = true
            let cgImage = try imgGenerator.copyCGImage(at: CMTime.init(value: 0, timescale: 1), actualTime: nil)
            let thumbnail = UIImage(cgImage: cgImage)
            self.mediaType.image = thumbnail
        } catch {
            print("*** Error generating thumbnail: \(error)")
        }
    }
    picker.dismiss(animated: true, completion: nil)
}
    You can write like...
if let image = info[.originalImage] as? UIImage {
    print("image found")
    //do something with an image
} else {
     print("Not able to get an image")
}
    info[convertFromUIImagePickerControllerInfoKey(UIImagePickerController.InfoKey)]
does not make any sense. You are specifying the whole enum type InfoKey instead of a specific value, e.g.:
info[convertFromUIImagePickerControllerInfoKey(UIImagePickerController.InfoKey.originalImage)]
Which can be probably also written just as:
info[.originalImage] as! UIImage
    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any])
{
    // Local variable inserted by Swift 4.2 migrator.
    let info = convertFromUIImagePickerControllerInfoKeyDictionary(info)
    if picker.sourceType == .photoLibrary || picker.sourceType == .camera
    {
        let img: UIImage = info[convertFromUIImagePickerControllerInfoKey(UIImagePickerController.InfoKey.editedImage)] as! UIImage
        EditedImage=img
        WAProfile_UserImageView.image=EditedImage
        picker.dismiss(animated: true, completion: nil)
    }
}
// Helper function inserted by Swift 4.2 migrator.
fileprivate func convertFromUIImagePickerControllerInfoKeyDictionary(_ input: [UIImagePickerController.InfoKey: Any]) -> [String: Any] {
return Dictionary(uniqueKeysWithValues: input.map {key, value in (key.rawValue, value)})}
// Helper function inserted by Swift 4.2 migrator.
fileprivate func convertFromUIImagePickerControllerInfoKey(_ input: UIImagePickerController.InfoKey) -> String {
return input.rawValue}
    You can access the properties as follows.
var editedImage = (info[UIImagePickerControllerEditedImage] as? UIImage)!
var originalImage = (info[UIImagePickerControllerOriginalImage] as? UIImage)!
    来源:https://stackoverflow.com/questions/50928934/swift-4-2-cannot-convert-value-of-type-uiimagepickercontroller-infokey-type