A content player can detect pirated content by storing a list of highly compressed content pieces that correspond to different pieces of content (e.g., audio content, video content, audio/video content, etc.). A piece of content to be played back by the content player is compared to the highly compressed content pieces stored at the content player. If the piece of content to be played back matches one of the highly compressed content pieces, then appropriate responsive action is taken. This repsponsive action can vary, and can include, for example, checking for a valid license, giving the user the option to notify the publisher if he or she has unknowingly acquired a pirated copy of the content, etc.