The Copyright Act distinguishes between useful articles (which are not eligible for copyright protection) and decorative and ornamental features of useful articles (which are eligible for copyright protection if they are sufficiently separable from the uncopyrightable product).
In the recent case of Star Athletica v. Varsity Brands, the U.S. Supreme Court eliminated the widely-held "physical or conceptual" separability test and replaced it with their own test:
"An artistic feature of the design of a useful article is eligible for copyright protection if the feature (1) can be perceived as a two- or three-dimensional work of art separate from the useful article and (2) would qualify as a protectable pictorial, graphic, or sculptural work either on its own or in some other medium if imagined separately from the useful article."
Melissa Kern at Frost Brown Todd posted an excellent article about this decision here:
http://www.frostbrowntodd.com/resources-in-fashion-this-season-and-also-eligible-for-copyright-protection-graphical-elements-of-clothing-designs.html
In the recent case of Star Athletica v. Varsity Brands, the U.S. Supreme Court eliminated the widely-held "physical or conceptual" separability test and replaced it with their own test:
"An artistic feature of the design of a useful article is eligible for copyright protection if the feature (1) can be perceived as a two- or three-dimensional work of art separate from the useful article and (2) would qualify as a protectable pictorial, graphic, or sculptural work either on its own or in some other medium if imagined separately from the useful article."
Melissa Kern at Frost Brown Todd posted an excellent article about this decision here:
http://www.frostbrowntodd.com/resources-in-fashion-this-season-and-also-eligible-for-copyright-protection-graphical-elements-of-clothing-designs.html