You need to prove publication of the work and that you filed the registration. If sent from your computer, or you have the original copies you mailed in, that should suffice.
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I agree with Attorney Doland. Keep in mind that in a lawsuit you will ultimately not be able to protect your identity.
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My colleagues are correct. I have received this question before and I generally have the same question that: what is the point of keeping your identity secret if you will eventually have to reveal yourself in litigation?
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I disagree with my colleagues. This is going to sound real picky but here goes: To enforce the copyright in court the Questioner does not have to prove either publication of the work or that he, personally, filed the registration.
What must be established is that the defendant had "access" to the allegedly infringed material and that the person [or company] that claims to own its copyright does, in fact, own the copyright.
Many suits are filed to enforce unpublished works [e.g., "MGM used the script that I sent them to make Batman"].
As for ownership, there is no requirement during litigation to disclose the name of the living, breathing author -- in fact, in work for hire situations, the hiring company IS the author of the work.
I agree that during discovery during the lawsuit the name of the living, breathing author must be disclosed. But if the copyright owner is a company, I can easily envision that fact being buried as irrelevant.
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