Stick on a fake moustache. Add some glasses. Dye your hair. And perhaps pop on a hat. If you are a man – or woman - on the run in the movies then this kind of low-tech disguise is all that is needed to evade the authorities.
But, in a case of life imitating art, a similar array of tactics seems to have met with some success in the real world.
One of the more bizarre news stories of recent weeks concerns John McAfee, founder of the eponymous anti-virus software company, going on the run from the Belize police. According to his blog, McAfee disguised himself by colouring his hair and beard grey, darkening his face with shoe polish, padding his cheeks with bubble gum and stuffing his right nostril to give it - in McAfee's own words, "an awkward, lopsided, disgusting appearance".
This rather theatrical approach to disguise apparently helped McAfee observe the police going about their investigations and evade detection until he made his way to Guatemala, where he surfaced earlier this week.
But, fugitives in the future may not have it so easy. Recently, the FBI revealed plans for its Biometric Identification Tools Program, which amongst other things, aims to develop mobile facial recognition software – allowing a field agent to “access the biometric identification power of the US Government, in real time, at any point on the planet”. In essence, it takes the kind of surveillance technology that is commonplace in streets, shopping centres and sports stadiums in Europe and the US, and allows it to be used anywhere in the world.
So would this kind of app succeeded in catching out McAfee? Probably not if it is based on current technology. In reality, facial recognition technology is still surprising clumsy. Some people do not need to do anything nearly as extreme as McAfee to fool facial recognition systems. In fact, they don’t need to do anything at all. That's because certain faces are just too "normal" for facial recognition systems to work with, according to Jean-Luc Dugelay, a video surveillance expert at Eurecom, a French research institution. "Certain people have faces that just seem to be hard for computers to recognize," he said. "It's difficult to know why, and the faces that are hard to recognize vary from one recognition system to another. But if you have something that is close to the average face, then it will be harder for a computer system to recognize you."
To understand why this might be, it's worth considering how most face recognition systems work. According to Anil Jain, a computer science professor at Michigan State University, they first have to work out that they are being presented with a face - a process known as face detection – and then move on to recognition and matching it with a face that is already known to the system.
Face detection usually involves detecting tell-tale "intensity signatures" of dark and light spots on an image that are typical of a human face. "Humans look for an oval for the face, with two eyes, a nose between them and a mouth beneath," Dr Jain explained. "Computers work in a different way: they don't look for physical features. Instead they may look for a horizontal pattern of dark, light dark, which corresponds to a line between the eyes."
Once a face has been detected, there are a number of techniques that can be used to recognize it. One way is to create a mathematical representation of the face - something known as a "feature vector - that is constructed from pieces of hundreds of "standard faces" in different proportions. These standard faces are known as Eigenfaces, and are themselves generated by analysing thousands of real faces using a process called principal component analysis.