Limitations of Copyright Protection

     Copyright protection is limited to protecting "expression" and does not protect the "ideas" embodied in the work. However, distinguishing protected "expression" from public domain "ideas" can be difficult, particularly with works such as computer programs. Courts often struggle with these issues and the legal rules are complex.
      To establish liability for copyright infringement, the infringing work must not only be substantially similar in some significant portion to the original work, but the accused infringer must have had access to the original work. Without access to the original work, there is no infringement, even if the two works happen to have portions that are identical.