The international problem of online child abuse is one that continues to challenge law enforcement agencies worldwide. PhotoDNA software offers some hope in the global fight against child pornography.
The Netherlands Forensic Institute (NFI) is currently trialing a program which could significantly enhance current methods for tackling online pedophilia. Developed in 2009 by Microsoft and Darmouth College, the PhotoDNA software has the capacity to search through large collections of images, automatically.
The software is already in use by Hotmail and Facebook. They use it to compare photographs uploaded to their sites with those held by the United States Child Victim Identification Program. The software is also being tested by the Netherlands Forensic Institute (NFI) in The Hague.
A unique signature
By converting an image to black and white, resizing it and breaking it into a grid, PhotoDNA makes it possible to detect images that are alike.
“In the same way that the characteristics of every person’s DNA are different, the signature of every photograph is also different,” Ton van Gessel, chief security advisor at Microsoft Netherlands told DW.
Even if both images have been altered, the mathematical technique used by PhotoDNA can determine whether two photographs are the same – that is, if they have the same DNA.
The current method used by Dutch investigators is one that reads an image’s unique, cryptographic hash. But this method can only match images that have not been altered.
When a child abuse image is downloaded, cropped, resized, or saved as a different file type, which is often the case in online child pornography, its unique signature – the cryptographic hash – also changes.
This makes the task of finding matches of photographs virtually impossible.
Professor Erwin van Eijk is the NFI forensic scientist leading its PhotoDNA trial.
He says it’s challenging enough to compare just one image against the NFI’s database of one million. It is even harder to compare thousands of images obtained from a suspect’s computer.
“We need to be able to filter a suspect’s images more efficiently,” van Eijk said.
Speeding up the process
Investigators will have to sift through terabytes of images themselves when no match is found – unknown images still have to be investigated. But it is hoped that PhotoDNA will speed up the process of investigating the trafficking of child abuse images. And if it is implemented by different countries, PhotoDNA could also help determine links between international pedophile rings.
Theo Noten, a spokesperson for Defense for Children, ECPAT Netherlands, says PhotoDNA helps to remove uploaded images of child abuse more quickly.
“For victims, it is important that this proof of their abuse is available on the internet for as little time as possible,” said Noten, “because the longer an image is available, the bigger the chance it will be replicated and distributed further.”
However, Noten says the effectiveness of PhotoDNA will be limited by the fact that different countries have different legislation on child pornography.
“International harmonization of legislation on what is considered child pornography is crucial. Also, sharing of all available databases at an international level is essential to speeding up the process,” Noten said.
Just the beginning
The NFI’s Erwin van Eijk admits the software is not perfect – particularly because it can only match known photographs. But he says PhotoDNA will set a standard.
In March, Microsoft said it would make PhotoDNA available for free to law enforcement agencies worldwide.
Van Eijk says he hopes all law enforcement agencies take up the offer.
“If you want to do something about child abuse you have to do this internationally,” said van Eijk
PhotoDNA results could soon be used as admissable evidence in a court – if the NFI’s trial is successful. The NFI expects to have its results by the end of September.
But van Eijk says PhotoDNA is just the beginning.
The NFI is the world’s first government body to be licensed to install PhotoDNA in its own software.
“Part of our work is to create new tools with PhotoDNA in them [to help] the digital analysis used to extract images from a large cache of unknown data,” said van Eijk.
The next step will be to develop a software like PhotoDNA for videos. Videos are “worse” because they contain 25 images per second. It’s something the NFI and Microsoft have started to investigate.