Scientists have developed a new computer tool that can predict how a person's facial features will change with age, an advance that will help search for people who have been missing for a long time.

Researchers from University of Bradford in the UK evolved a method that maps out the key features, such as the shape of the cheek, mouth and forehead, of a face at a certain age.

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The technique uses a method of predictive modelling and applies it to age progression.

The model is further strengthened by incorporating facial data from a large database of individuals at different ages thus teaching the machine how humans actually age.

Researchers used a method called de-ageing whereby they take an individual's picture and run their algorithm backwards to de-age that person to a younger age.

A key feature of the method is that it teaches the machine how humans age by feeding the algorithm facial feature data from a large database of individuals at various ages, said researchers of the study published in the Journal of Forensic Sciences.

They then compared the result with an actual photograph of the individual taken at the young age.

As a test case, researchers chose to work on the case of Ben Needham. He disappeared on the Greek island of Kos on July 24, 1991, when he was only 21 months old.

He has never been found, but several images have been produced by investigators showing how Ben might look at ages 11-14 years, 17-20 years, and 20-22 years.

The team used their method to progress the image of Needham to the ages of six, 14 and 22 years. The resulting images show very different results, which the researchers believe more closely resemble what Needham might look like today.

An effective method needs to do two things, the synthesised images need to fit the intended age and they need to retain the identity of the subject in age-progressed images, researchers said.

The results were evaluated using both machine and human methods, and in both, the images of Needham produced using this method were found to be more like the original picture of Needham than the images created as part of previous investigations.

"We are presenting our work as a development and improvement that could make a contribution to this important area of police work," said Hassan Ugail, professor at University of Bradford.

"We are also developing further research plans in order to develop this method so it can be incorporated as a biometric feature, in face recognition systems, for example," Ugail said.