Science: Growing older before our eyes: Missing people can be found with the help of computerised images. Bernadine Coverley reports

Maureen walked out on her husband and two daughters three years ago. Norma went to babysit but never arrived. Kevin, 16, went to buy eggs for a cookery exam in 1986 and did not return.

The files at the National Missing Persons Helpline (NMPH) make sad reading. About a quarter of a million Britons - men, women, teenagers, and, rarely, children - are classified as 'missing persons' at any one time. Most turn up or are traced, although not all want to renew contact with friends and family. Investigations in the Cromwell Street case in Gloucestershire have drawn attention to the tragic fate of a few and to the ordeal endured by their families.

The NMPH - which changed its name in March from the Missing Persons Bureau to distinguish it from the new police register of the same name - was set up in 1989 and granted charitable status two years ago. It has developed rapidly. One volunteer, Di Cullington, has access to pounds 30,000 worth of computer technology which enables her to produce updated photographs showing how people are likely to have aged in the years since they went missing. This gives an indication of how a missing person may look now and thus assists in the search.

'I only work on cases where the police are involved, to get renewed publicity for cases that have gone cold when someone is missing long- term,' she says. 'It needs public interest to find fresh information.'

The process of charting age progression involves 50 per cent technology and 50 per cent artistry. The Wang PC 480, with its high-resolution screen, and the PhotoSketch program - developed by QMA- Infotech and donated by the National Center for Missing & Exploited Children in the United States - take care of the technological side of things. Mrs Cullington uses her artistic ability and knowledge of anatomy to do the rest.

'The computer allows me to manipulate a photographic image. It doesn't do it for me. The age enhancing of a child has to start with the bone structure as that is still growing. There is a tremendous amount of facial change between two years of age and 13 for a girl, 14 for a boy. After that the age changes are from the outside,' she says. She starts by scanning in a photograph using a colour video scanner, then adds photographs of close family members taken at the age the child would be now.

Three years ago Ben Needham was abducted from the garden of the family villa on the Greek island of Kos. He was 21 months old. An age-enhanced photograph portrays a four-year-old Ben on the updated poster, part of a fresh publicity drive after reported sightings.

The new photograph, which is based on an old one of Ben, includes features merged in from a photo of his mother as a child and shows a smiling boy with clothes and haircut typical of a four-year-old.

'Being able to look at the details of a picture on a large screen means I can see things that are not obvious on a small snapshot,' Mrs Cullington says. 'The family may take moles or a small scar for granted and forget to mention them but it is those things that make the 'aged' photo an individual rather than a look-alike.'

As she demonstrates the 'stretching' process, a child's face comes up on screen with four small reference pictures down one side. A grid is overlaid and the delicate work of enlarging the face begins. Each square is gently pulled using the mouse, building up the bridge of the nose and lengthening the face.

Then certain features from a sibling's or parent's photograph of the appropriate age are brought through to merge with the main picture. If, as in this demonstration, the person in the photograph is smiling, the facial muscles have to be altered. Then the newly age-enhanced face is matched with the relative's by bringing half of each face on to the main screen. If the new image is by now a recognisably older version, then it is time to go to the pixel zoom window where 60 shades from black to white show the contour shadows and smile crinkles.

'I'll just put a couple of highlights on the eyes to go with the smile, enlarge the teeth a little and take out the plumpness that came with the smile,' Mrs Cullington says. 'The final touch is to merge the right-age clothes from reference photos and to check haircuts. A young child will almost certainly have a fringe if the hair is straight.'

On the wall over her desk two photographs bear witness to the effectiveness of her work. One - which has been age-enhanced - appears on a 'Missing' poster and the other was taken after the seven-year- old was home again. The only discernible difference is the crooked teeth in the latter. 'He didn't have a very good diet,' she says.

The NMPH dealt with 30,000 calls last year and helped trace 350 people. And, thanks to co-operation between the charity and police officers, 90 families have been reunited with missing loved ones since the start of investigations in the Cromwell Street case. The police turned to the NMPH for help because, up until two months ago, they had no central record of missing persons.

Mary Asprey, a founder of NMPH, says: 'We hold information on all missing perons, not just those considered vulnerable, and it is this that is useful to Gloucester police.'

But there have been other, decidedly frivolous, requests for age-enhanced photos. Mrs Cullington says: 'I've been asked what Prince William will look like when he's King. But my answer is that it is not a toy.'

The National Missing Persons Helpline number is 081-392 2000

(Photograph omitted)