Most things in the world including people have some feature or combination of features which are unique to that item. These features if they can be recorded in some way can be used as a means of identification. It is even possible under some circumstances to ADD features to objects as identifiers.
As the term implies this identity is based on the measurement of some unique feature in living entities, normally human beings. We all have unique feature which can be captured and used as comparisons for identification, e.g. finger prints and Iris patterns.
Finger Print - Finger print readers are now very common, and used in a variety of applications. Many laptop computers now have built in finger tip readers as a security device either instead of or as well as the normal password protection.
Palm Vasculature - The pattern of veins in the hand is a unique feature, which can be captured by "photographing" reflected infra red light. Some readers require contact whilst others can read the palm from a few inches, making them ideal where sterile conditions are needed such as electronic clean rooms or hospitals.
Iris Recognition - The patterns within the iris are also a unique feature of every individual and can be used as proof of identity. The system is normally used on entry devices to very high security installations. They can be used in isolation or often in combination with finger print or palm print devices.
Facial Recognition - The relationship between various standard measurements within the human face, when taken over a series of standard reference points is rare enough to be used as individual identity with a very high degree of certainty.
Handwriting Recognition - In the simplest instance this can be used as a proof of identity by matching a signature against a known standard. Increasingly sophisticated systems can be used to capture data into database systems in a readable form by "translating" handwriting into typed text, with ever increasing accuracy, often using adaptive computing techniques.
Speech Recognition - As with handwriting, speech recognition was originally used forensically and for identification purposes only. Increasingly it is being used as a means of direct entry to computer systems, via "Voice to Text" systems, either directly via microphones or even by plugging in personal dictation devices. Adaptive technologies increase the accuracy of such systems.
Feature recognition can also be a valid identification method for objects as well as for people. In some instances natural features can be used whilst in other situations specific features may be added.
Geometric Conformity - It is possible by the use of high definition cameras to compare shapes against specifically captured images. This technique is used extensively in Quality Control applications for checking products whilst moving on production lines. Examples might be:- checking machining detail, or even checking for cap closure on bottles.
Electronic Noses - Very sensitive devices can measure the presence of minute combinations of volatile liquids, for example SO2 ammonia etc. There can be applications in perfume manufacture, and also the sensors can be used to judge the ripeness, or rottenness as the case maybe, of fruit.
Thermal Imaging Many objects have a thermal fingerprint which is rare enough to be used as identification. This may be used to judge the "status" of an item as well as the item itself. It is another technique that can be used for judging the freshness or not of substances such as food.
Laser Speckle Analysis - Most surfaces, even those thought of as smooth, such as plastic, have a texture, which at any point on the surface can be considered unique. For example paper has randomly distributed strips of cellulose. If a laser is projected onto such a surface the unique reflection can be captured as a unique "speckle" pattern by a digital camera and used as an identity. Typically a specific part of a passport could be recorded, which means forgery would be impossible, because the speckle pattern on the forgery would not match the original.
It is possible to add inert chemicals into substances, called taggants which allow for identification. These can be of a chemical or a bio-chemical composition. These elements would normally (but not exclusively) be detected by some form of chromatography.
One of the first uses of such taggants was the identification of explosives such as Semtex. The substance which is almost unidentifiable in its natural state has added to it two types of identifier. It has a detection taggant which is a low volatility substance which evaporates very slowly but its odour is strong enough to be detected by specially trained dogs that can identify the fact that it is Semtex, but not its origin. Post explosive taggants in the form of long chain molecules are also added which survive the explosion, but are recognisable in particular combinations to a country of origin, and a batch number.
Other typical applications for taggants would be identification of liquids. In particular oil in tankers may have a specific combination of chemicals added in tiny but measurable quantities to identify and validate its well of origin. These taggants can be to defeat counterfeiting or piracy, and as proof of duty paid at various stages in the life of the oil. In some instances where identification has to be guaranteed unique synthetic DNA may be added.
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