Most of the media you encounter is protected by copyright law. Many of these materials are also designed to prevent you from easily copying or manipulating them. “Cracking” these materials and copying them falls into some legal grey areas. However, there are “fair use” exceptions to copyright. Using copyrighted material may be permitted if you are engaging in activities like parody, criticism, teaching, and transformative work.
Copyright and fair-use are complicated. Typically, determining fair-use happens on a case by case basis. There is no easy set of rules to guide your actions and choices. If you want to practice remix and produce media that utilizes pre-existing source materials, it is critically important that you educate yourself about fair-use and intellectual property law.
Here are some useful places to start:
Fair Use FAQ (from Electronic Frontier Foundation)
Center for Media & Social Impact’s Code of Best Practices
in Fair Use for Online Video