If you've been accused of violating someone's copyright, you can be in deep trouble with the law if you don't defend yourself right away. Your attorney can help you decide on a number of potential defensive options, from admitting to copying a person's work to denying that you've ever seen the work in the past.
Copyrights that are invalidated won't stand up in court, so the first thing you may want to discuss is whether the copyright is legal. If the person's work wasn't original or if the copyrighted material lacked a copywritable subject, then you may be able to have the case dismissed.
For example, a person could claim you stole an idea about a story he or she was writing, but if that story is in the public domain, then anyone can use it without violating anyone else's copyright. Likewise, if the person who claims you've violated copyright doesn't own the work, then there is no case to be made.
If you admit to copying someone's work, you may be able to show that you did so on such a small scale that it has no effect on the copyright holder. For example, Disney has many characters that have been copyrighted, but the company is unlikely to want to pursue a claim against an individual who uses a character for a charity event or other situation where there has been little, if any, damage to the company due to the character's use. It would be within its rights to seek a lawsuit, but that would be unnecessary, and the defense could raise several arguments.
Source: UNC.edu, "Defenses to Copyright Infringement," accessed Dec. 22, 2016