如何避免将照片替换为Firebase存储

Question

每次上传重命名时如何获取myImage.png，以免在Firebase存储中被替换？

    let storageRef = Storage.storage().reference().child("myImage.png")
    if let uploadData = UIImagePNGRepresentation(self.myImageView.image!){

        storageRef.putData(uploadData, metadata: nil, completion:
            {
                (metadata, error) in
                if error != nil {
                    print("error")
                    return
                }