A forensic artist who "age enhanced" an image of Madeleine McCann, the young girl who disappeared while on a family vacation in Portugal, needed to combine her knowledge of anatomy and forensics with a little bit of artistry.

"It’s not quite as straightforward as putting a whole bunch of photos in [a computer], pressing a few buttons and out it pops," Teri Blythe told CBC News in a phone interview from her U.K. home. "It's using the training I have, the experience I have and knowledge I have of how faces change. But it's also using the artistic side of it to actually manipulate photos into a new face."

Blythe was asked by the Metropolitan Police Service to create the image, which was made public ahead of Madeleine’s ninth birthday on May 12. Madeleine has been missing since she disappeared a few days before her fourth birthday from a holiday apartment at the Ocean Club in Praia da Luz on May 3, 2007.

Face-aging software

A forensic artist isn't always needed to create an age-enhanced image. Toronto-based Aprilage Development Inc. has created face-aging software that uses a picture of an individual along with information about the person's age, sex and ethnicity.

That information is compared with the company's database of thousands and thousands of head scans. An average of that data is applied to the person's face and an age-enhanced image is created.

The software, which has been primarily used to show the affects of smoking and obesity, is currently being used for an exhibit at the Ontario Science Centre. But the company's website also allows people to send in a picture to be age enhanced.

A number of law enforcement agencies make use of age progression technology when looking for missing children, and it has been used in high-profile cases such as that of Jaycee Dugard, the California girl who was kidnapped at age 11 and held captive for 18 years.

For example, the RCMP’s National Missing Children Services offer a computer photo age progression service, in which a trained forensic artist helps create a portrait, using photographs, of what a missing child might look like today.

Blythe, whose academic background is in human anatomy, forensic anthropology, and facial imaging, has been a forensic artist for 10 years. She worked with Britain’s Missing People Charity and received training at the Virginia-based National Center for Missing and Exploited Children, as well as the FBI and London police.

She said she uses basic photo manipulation software on her computer, the kind of program that anyone has access to.

Blythe said she starts by collecting as many photos as possible of the missing person, including recent photos of the family.

"Basically you’re looking for direct family members," she said. "I don’t tend to look at aunts or uncles or grandparents because they're an extra step removed."

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The top image shows a picture of Jaycee Dugard around the age she was kidnapped while walking to school. The middle picture, released by Natational Center for Missing and Exploited Children, shows an age-enhanced image of Jaycee created in 2006. The bottom image is a picture of Jaycee in 2012. (Top image - Carl Probyn/AP - Middle image - NCMEC Bottom image - Andrew H. Walker/Getty Images )

Getting information from the parents, if possible, can be key in creating an age-enhanced image of a child, she said.

"Who did they look like, who did they not look like, which features are similar —  that kind of thing. So when I'm changing the image I can bear that in mind."

For Madeleine, Blythe said, she had access to a large range of photos of the girl and her family and used the whole range for reference.

She used not only recent pictures of her parents, but snapshots when they were young and at age nine, which would be Madeleine's current age.

"For a child especially, it’s not only superficial things that are changing, but obviously the skull is still growing and the teeth are changing — that kind of things. Using reference photos against parents will at least give us an indication of the right proportion of the face."

Blythe looks for the best and clearest image available of the missing person.

Once she has the pictures, Blythe begins using the software to manipulate the photo, stretching the face to the right proportions for that age while trying to maintain the key features of the individual to make sure they are still recognizable.

Generic clothing and hairstyles are also used to avoid distracting from the face, she said.

At a certain stage in the process, she solicits feedback from the family members to make sure they can still recognize their child.

"And if they have any comments like ‘We think she looks more like so and so and we think her nose would be longer.’ Any of those kinds of details are helpful to get from the family, then I can make extra tweaks to the image."

Blythe said that with Madeleine, once she completed the first stage of aging, she sent the image to the family. She said they were able to suggest details or tweaks they thought would improve the likeness.

"Once we had worked on this they were happy with the result, but of course, as you can imagine for any parent, this is very strange process to go through," she said.