“The idea–expression divide or idea–expression dichotomy limits the scope of copyright protection by differentiating an idea from the expression or manifestation of that idea.”
In Baker v. Selden, 1879, the U.S. Supreme Court first spoke of the difficulty in separating facts and originality — now known as the idea-expression divide.
The court held that an idea (the facts, concept) can be protected by patent law but not copyright law, which is for the expression (the description, prose) of the idea. The doctrine was further stated in the landmark Harper & Row v. Nation Enterprises, 1985.
“copyright’s idea/expression dichotomy ‘strike[s] a definitional balance between the First Amendment and the Copyright Act by permitting free communication of facts while still protecting an author’s expression.’” [quoting the appeals court]
— U.S. Supreme Court, in Harper & Row v. Nation Enterprises, 1985
“Unlike a patent, a copyright gives no exclusive right to the art disclosed; protection is given only to the expression of the idea — not the idea itself.”
— Mazer v. Stein, 1954
In pictorial art, however, it can be hard to discern the idea from the expression.
“In the context of photography, the idea/expression distinction is not useful or relevant.”
— Mannion v. Coors Brewing Co., 2005
“The idea/expression distinction arose in the context of literary copyright.  For the most part, the Supreme Court”
— has not applied it outside that context.
“one cannot divide a visual work into neat layers of abstraction in precisely the same manner one could with a text."”
— Judge Newman discussing Warner Bros. v. American Broadcasting Companies
“it is not .. the idea of a couple with eight small puppies seated on a bench that is protected, but rather Rogers’ expression of this idea — as caught in the placement, in the particular light, and in the expressions of the subjects..”
— Rogers v. Koons
“The idea/expression distinction in photography, and probably the other visual arts, thus achieves nothing beyond what other, clearer copyright principles already accomplish. .. In the context of photography, the idea/expression distinction is not useful or relevant.”
— Mannion v Coors Brewing, 2005
“The distinction between an idea and its expression is an elusive one.”
— Williams v. Crichton, 84 F.3d 581, 587-588 (2d Cir.1996)
“Gentieu cannot claim a copyright in the idea of photographing naked or diapered babies or in any elements of expression that are intrinsic to that unprotected idea. Clearly the `poses’ at issue in Gentieu’s images capture the natural movements and facial expressions of infants.. Such poses are implicit in the very idea of a baby photograph and are not proper material for protection under Gentieu’s copyrights.”
— Gentieu v. Tony Stone Images/Chicago, Inc., 255 F.Supp.2d 838, 849 (N.D.Ill.2003)