Forensic identification

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Forensic identification is the application of forensic science and technology to identify specific objects from the traces they leave, often at a crime scene.

People can be identified by their fingerprints, from traces of their DNA by DNA fingerprinting, from their teeth or bite by forensic odontology, from a photograph or a video recording by facial recognition systems, from the video recording of their walk by gait analysis, from an audio recording by voice analysis, from their handwriting by handwriting analysis, from the content of their writings by their writing style (eg. typical phrases, factual bias, and/or misspellings of words), or from other traces using other biometric techniques.
Firearms can be identified by ballistics from the marks on the bullets they fired and on the bullet cartridges.
Documents are characterized by the composition of their paper and ink.
Typewriters can be identified by minor variations of positioning and wear of their letters.
Paper shredders can be potentially identified in a similar way, by spacing and wear of their blades.
Color copiers and maybe some color computer printers steganographically embed their identification number to some printouts as a countermeasure of currency forgeries.
Copiers and computer printers can be potentially identified by the minor variants of the way they feed the paper through the printing mechanism, leaving banding artifacts. [1] [2]
Social networks can be discovered by network analysis of banking, telecommunication and postal records.
Radio transceivers can be potentially identified by minute variations of their output signal.
Cars can be automatically found on CCTV records by automatic number plate recognition.
Computers connected to the Internet can often be identified by their IP address or MAC address.

Sometimes, manufacturers and film distributors may intentionally leave subtle forensic markings on their products to identify them in case of piracy or involvement in a crime. (Cf. watermark, digital watermark, steganography.)