From the official www.copyright.gov page:

"No publication or registration or other action in the Copyright Office is required to secure copyright. Copyright is secured automatically when the work is created, and a work is “created” when it is fixed in a copy or phonorecord for the first time. “Copies” are material objects from which a work can be read or visually perceived either directly or with the aid of a machine or device, such as books, manuscripts, sheet music, film, videotape, or microfilm."

"The use of a copyright notice is no longer required under U. S. law...", though these statements I have made are intended as official notice having been presented as of the stated date of (online) publication.

"To be eligible for copyright for that portion which is derivative work, content must differ sufficiently from the original to be regarded as a new work, or must contain a substantial amount of new material."