Check if copyrights for files are complete



I am trying to create a Drupal module which checks if all uploaded files (images, videos, audio files) have been copyrighted. In the past, this was easy because all I had to do was check whether the copyright on files was filled. It is now very different whether the content types use the copyright or the metadata. Some content types also use both for different elements.

Is there a PHP method that returns if there is a copyright on every file? Or is there another way for this check?

Thanks for support!