“Photo DNA” – How reliable is it?

PhotoDNANo one can doubt that sexual crimes against children are among the most horrific imaginable. And given the obsession that lawmakers have with sex crimes and the punishment of anyone associated in any way with them, it’s not surprising that the market has responded with the creation of new technologies designed to help catch the people involved in Internet child pornography. A Swedish company has been quietly amassing a huge database of over 400,000 images and videos of what purports to be child pornography. They don’t clarify how they define this or how they determine if the original photos are of real children or simply digital creations, but they have combined forces with Microsoft’s “Digital Crimes Against Children” group  (did you know that Microsoft had such a group?) and produced something they call “PhotoDNA”, designed to help law enforcement catch the bad guys creating, distributing and viewing this stuff.

The goals are laudable, but because this is a one-side effort (Microsoft makes this available to law enforcement only, and not to the defense), there is no way for an objective observer to determine the answer to many critical questions. Capitalizing on public perceptions that DNA is infallible and scientific, the name alone creates presumptions that cannot be tested by the defense. The technology purports to identify a photograph’s “digital fingerprint” based on a hash algorithm which can then be applied to other suspect images to see if the suspect image is derived from, or identical to, the original image. Here’s what Microsoft says about the process:

“PhotoDNA uses a mathematical technique known as robust hashing that works by calculating a unique signature into a ‘hash’ that represents the essence of a particular photo. In the same way that the characteristics of every person’s DNA are different, the signature or ‘hash value’ for every photo is different, enabling the creation of a hash that can identify an image based on its unique characteristics or its ‘digital DNA.’ Although a photo’s hash cannot be used to re-create an image or identify people or items within an image, it can be compared with hashes of other photos as a reliable way to match two different copies of the same image”.

Several important questions arise. Have scientific validation studies been performed that have produced a reliable error rate for this technology? Even a DNA scientist will tell you about error rates. It is impossible to judge the value of a given technology without knowing the error rate produced when that technology is used in the field. Second, the technology claims to identify an image as originating with another image based on the similar hash value, but how do we know that the original image is authentic? What if that original image was photoshopped to begin with? And since this whole thing is driven by Microsoft software, does anyone really believe that the software implementation of the hash algorithms are 100% bug free?

The problem is compounded by the fact that neither Microsoft nor NetClean makes any of this technology available to the defense, just to law enforcement. Why on earth would anyone interested in getting at the TRUTH want to withhold from the only community that is charged with keeping the government honest? It’s shameful when companies discriminate against the defense and demonstrate their indifference to the real, well-documented reality that innocent people ARE convicted of crimes they did not commit. That’s what real DNA has taught us. This faux DNA, that seeks to ride the coattails of real science, is a good start at helping eradicate a very real problem in our society, but it becomes dangerous when its advocates refuse to shine the harsh light of scientific scrutiny on it. What are they afraid of?

See the joint Microsoft-NetClean video on PhotoDNA  here.

– RP


Whether you know it or not, it *does* happen.

Cameron Todd Willingham was a family man. He loved his wife and his children and he worked hard. When his Texas home caught fire one night, neighbors reported seeing him frantically running in and out of the house trying to save his family. He was heard shouting “my babies are in there, my babies!”, and was scorched running in and out of the flaming house. Unfortunately, the heat overcame him and he was not able to save his children and they died in the fire.

willinghamInvestigators found evidence of what was then known as “spidering” on the glass in the house, a web-like cracking of glass that is often associated with the use of an accelerant, like gasoline. Police noted some inconsistencies in Willingham’s account of the incident and apparently gave little weight to the hysteria of the moments that led to Willingham’s confused statements. Prosecutors charged Willingham with arson and murder and he was convicted by a jury. Throughout the entire proceeding he maintained his innocence and insisted he had nothing to do with the fire that killed his family. Based on this conviction, Willingham was sentenced to death row in Texas.

When the Innocence Project got involved they brought in nationally renowned arson experts from around the country who disputed the findings of the original “expert” who testified at trial. The most astonishing finding of the outside experts was that the so-called “spidering” effect is often caused by the application of cold water to hot glass which, of course, is exactly what happens when fire trucks arrive at a house fire and attempt to douse it with water. The consensus among the experts was that there was “no scientific foundation” for a finding of arson. This conclusion essentially refuted the only significant evidence against Willingham and left experts to conclude that Willingham was factually innocent.

Unfortunately, this finding did not help Cameron Todd Willingham because it came *after* the State of Texas executed him for a crime he did not commit. Willingham continued to insist that he was innocent up to the day that he died, announcing at his execution that “Today the State of Texas is executing an innocent man”.

When you hear about executions like the ugly and failed attempt in Oklahoma last week, keep in mind that the mistakes we make are not just in the methods we use to kill prisoners, but sometimes in the very process we use to determine their guilt. And whether you know it or not, the fact is, innocent people ARE convicted more often than you think and, in some cases, put to death, for crimes they did not commit. Think about that for a minute and about all the cases the Innocence Project has not been able to investigate.

Read more about the facts and the mythology of the Cameron Todd Willingham case here.

– RP


There is no such thing as a LIE DETECTOR

liarDespite heroic efforts to find the holy grail of TRUTH, science has never effectively found a way to detect deception. There are of course polygraphs and it’s well known that they are inadmissible in court virtually everywhere as substantive evidence of deception. There’s a reason for this, and it is well documented at sites like www.polygraph.com, where the “junk science” behind these machines is exposed and effectively debunked. Why, then, does the FBI still routinely use them to interview suspects and employees, and why do so many law enforcement agencies use them during investigations? Simple. They provide a convenient cover for what is really an interrogation. The FBI will tell a suspect that they plan to administer a polygraph to “clear the suspect” and, instead of the typical 3-5 question session, they go on for six to eight hours with questions that far exceed the scope of any standard polygraph, and are really just used to justify further questioning (“the machine says you’re lying, and machines don’t lie”).

But the search for truth continues and scientists continue to explore the concept of a reliable method of detecting deception. One recent development is the notion of capturing “micro-expressions”. The idea here is that our initial reactions to news or questions, causes involuntary physical reactions that we cannot consciously mask, even if they only last micro-seconds. If we can capture these initial slices of human behavior, so the theory goes, perhaps we can find some uniform reactions that reliably reflect deception. It sounds like a real stretch to me, and at the end of the day someone is still going to have to make some kind of subjective judgment call as to what physical reactions reflect deception, but it does seem like something that could be empirically tested, so the application of a rigid scientific methodology in validating this hypothesis is welcomed.

But don’t get your hopes up. Or your fears. Read more in this New Yorker article.

– RP

Ohio Lab Director resigns

Scientist or cop? You decide.

If you’ve ever wondered what it takes to be the Director of a Crime Lab, where decisions are made regarding the science, preservation, analysis, and storage of life-changing forensic evidence, consider the case of Rick Perez (no relation, honest), 57, who worked in law enforcement for 37 years and served as Chief Deputy Sheriff of Stark County, Ohio. The job posting called for academic degrees in chemistry, forensic science or business management. Perez sailed through and got the job without any college degree. Science, schmience!

After this was brought to light, the mayor — who initially supported Perez for the position — “removed” Perez from the job and commented that it wasn’t about Perez, but about “the process”. In other words, it’s ok for cops to put on lab coats and manage scientific evidence, so long as nobody notices.

Read more about this here.

– RP