What is "mug book"

n. A book containing mug shots, pictures of faces.

n. a file of mug shots (pictures of criminals that are kept on file by the police) [syn: mug file]

A mug book is a collection of photographs of criminals, typically in mug shots taken at the time of an arrest. A mug book is used by an eyewitness to a crime, with the assistance of law enforcement, in an effort to identify the perpetrator. Research has shown that grouped photos result in less false-positives than individually displaying each photo.

Mug book also has a meaning in genealogy and history, referring to local biographical histories published in the US in the late 19th century.