just a little information about copyright:
as soon as you create something 'original,' you own the copyright. You can file your copyrighted creation with the government, but it's not necessary (and it doesn't grant you any extra protection). Writers/Comic book artists/programmers used to mail themselves copies of their work so the USPS would put an legal date on an unopened letter or package containing the work because it was cheaper than filing anything with the US copyright office. Sealing envelopes with a notary's seal on it was another common, cheap method of legally obtaining an official date on materials. Email things to yourself provides about the same amount of protection.
5th Cell/WB wouldn't be dumb enough to claim that they invented keyboard cat, regardless of when the copyright was filed, since keyboard cat as a meme predates their publication of the property(or wether there is no copyright, which is what they would argue if they wanted to drag the suit out--they're probably not dumb enough to say that they created keyboard cat). Keyboard/Nyan Cats may not be an 'original' enough ideas for them to warrant copyright protection, or the works might be copyrighted but scribblenaughts might be able to legally use them through "fair use" (another hugely legal grey area) , though--which a lawsuit may or may not provide a ruling on.
copyright/patent law is a fucking mess. You're only protected for as much as you have the means to defend your claim in court, which means that it just becomes a matter of who has more money to waste on lawyers.