If you submit electronic files e.g., digital photographs on a CD to the US Copyright Office as part of a copyright application, the Copyright Office stores your CD but does not transfer the files on it to its computers or other durable media. There is also no way to resubmit or otherwise replace electronic files stored in the Copyright Office archives if the magnetic or optical media you submitted them on deteriorate.
This appears to mean that the registrations for many copyrighted photographs will become legally indefensible if/when the CDs on which the images were submitted deteriorate. The person with whom I spoke at the Copyright Office suggested submitting photographic prints or contact sheets rather than CDs. This suggestion would have been good advice until recently, but it’s impractical for people who copyright large numbers of digital photos.
That sounds problematic.