Take a look at the evolution of U.S. formalities, especially as represented in concise chart form on pages 12-13 in Jane Ginsberg’s “The US Experience with Copyright Formalities: A Love/Hate Relationship”
Columbia Public Law Research Paper No. 10-225, posted for free at SSRN.It is especially useful in detailing deposit requirements, and the effect of recordation of transfers. Also takes a look at alternatives to registration wrt “marking off” ownership rights a la Creative Commons, noting that the DMCA prohibits the removal of such digital ownership markings. Brief look at what copyright examiners focus on, when approving copyright registrations. Overall an informative read. Recommended.