Copyright is automatic in the US, but there is a form to register a copyright with the Library of Congress and registration is a prerequisite before suing for s

Copyright is automatic in the US, but there is a form to register a copyright with the Library of Congress and registration is a prerequisite before suing for statutory (as opposed to actual) damages for infringement. A "timely" registration has a presumption of validity, but you can register at any time, including just before filing a lawsuit. This, for obvious reasons, won't enjoy as many presumptions as one registered soon after the work was made.