Yesterday, a federal court judge in New York ruled that Fantastic Four, Incredible Hulk, and X-Men, which were created by Jack Kirby, were done as "works for hire", and that Marvel Comics (now owned by Disney) retains the copyright to all such works.
Work for hire is the same legal principle which holds that characters you create, or rather, effects you originate, belong to the guy who pays you.
Ironically, the Major Studios include in every single contract an acknowledgement by the artist that the work they do is a "work for hire" and that the entity paying the bills will own the copyright. In the event that a Court finds the individual to be an independent contractor rather than an employee, the contract requires that individual to "assign" the copyright.
So, the Studio play it both ways. They argue that artists such as you and composers and lyricists are independent contractors and not employees and therefore not eligible to the protections accorded under federal and state labor law, but, for purposes of copyright they are certainly employees and their work-product belongs to the nice people paying the bills.
Coincidentally, in Canada, the writer owns and retains the copyright to the script they write. They cannot, under the Canadian writers guild agreement, give up that copyright; but can "license" the limited right to film a derivative work such as a film or television episode based on that script. But the writer retains all other ancillary rights to that script.
There is a small group in the WGA who have long fought to get similar copyright ownership pursuant to the AMPTP/WGA Basic Agreement. You should the studios turn purple when that topic comes up at the negotiating table!!
While it is unlikely that visual effects artists will ever control the copyright to their work product, the IATSE can, and will, make sure that you are properly represented, compensated, and recognized for the creative contribution you make.
I knew my background as an entertainment lawyer would come in handy one of these days.