Copyright infringement presents a serious issue for many artists- especially in their portfolio samples. The basic rule of thumb is: don't use anything that doesn't belong to you.
A copyright specifies who owns the right to copy a certain piece of work. Usually, this is the creator, however in cases where work has been created by an artist working for someone else or a company, the person signing the paycheck retains the copyright to the work.
Every artistic industry has a unique set of copyright issues. On an actor's reel, the performer must respect the rights of the playwright. In an animation reel, the animator may not present any work from a project funded by a larger production company. Even sources in academic portfolios must be properly cited.
- Overview of US Copyright Law
- Protecting your work against copyright infringement