What is the legal protection afforded an expression of an idea, such as a song, book, or video game?

First, apply for a copyright or a patent (depending on which of the above you are talking about).  However, that takes time.  You can consult an intellectual property lawyer.  If you can't afford one, you can use one of the free legal advice websites that will let you "chat" with a lawyer or law student in a specific area of law at no charge.

These traits are all equally important in recognizing the validity of artwork mainly due to an artists' consistent style and reputation which they have developed over a lengthy period of time. most famous paintings contain specific characteristics of the artist who created it. an appraiser would pay close attention to certain key elements within the painting, as well as an accuracy in measurement and color shade. blended textures and outlines are essential in recognizing an authentic piece from a copy. signature and imagery exist in epic proportions to balance out each trait as they coexist in harmony, depending on preference and style of each artist. no two original pieces are virtually identical, although it may be almost impossible to see discrepancy with the naked eye.