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Security technology:A、new type of computerised photofit system takes a novel evolutionary approach to generating images of suspects. If you have ever tried to describe someone’s face in detail, you will understand why the "photofit" composite images used by the police look so dodgy. In recent years, computerised "E-Fit" systems have helped improve the accuracy of these images by allowing witnesses to choose from a wider range of facial features.But researchers at the University of Stirling in Scotland found that, despite these improvements, people still have a hard time constructing recognisable faces--especially if there is a delay of more
The problem is that people tend to recoguise faces as whole entities, rather than as separate features. So picking from a range of eyes, noses and mouths is not necessarily the most suitable approach, saysCharlie Frowd, a psychologist at the University of Stifling. Next year, however,British police are expected to begin trials of a new computerised system, calledEvoFIT, developed byDr. Frowd and his colleague Peter Hancock. It uses an evolutionary approach, known as a genetic algorithm, to "evolve" faces rather than piece them together.
"The process is entirely non-verbal and takes a fraction of the normal time," claimsDr. FrowD、A、witness is shown an array of 60 different faces with random features. Having studied them closely, the witness is asked to choose the six images that most closely resemble the person they are trying to describe. These six are then used to generate another set of 60, by switching featurees between some of the images and by making random changes to others. The witness is then asked to repeat the task, whereupon a new batch of faces is generated, and so on. In evolutionary terms, this process is known as "genetic crossover and mutation", and is a powerful way to search a large number of possibilities for a particular solution.By allowing the user to steer the selection process, the program is able to generate a good likeness for the original face after just a few cycles.
In one of its early versions,EvoFIT was used by police in Northampton shire who were trying to catch a violent attacker. The attacker was never caught, but the senior investigating officer, Superintendent Paul Spick, says the witness involved found the new software much quicker and easier to use than traditionalE-Fit systems. It was also more accurate: the final image caused the witness visible distress when displayeD、A、further important advantage ofEvoFIT over traditional composites is that an image can be generated even if the witness can only provide a sketchy verbal description.
The researchers have since made a number of further improvements to their system and are now in the process of commercializing it in partnership withABM, aBritish firm which supplies police forces with photofit, one of the leading computerized composite systems. The images are more realistic, and the system can generate three-quarter angle views of the face, which are easier to distinguish than direct frontal views, saysDr. FrowD、
His team has also found that by combining the images generated by different witnesses, or even from a single witness, it is possible to get an even better likeness. 
This could be particularly useful when multiple witnesses come forward and the police are unsure which of the images they produce is the most accurate. 网考网解析：
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