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A man points to a mini camera hidden in a picture
Photo: JUNG YEON-JE / AFP
Spy cameras are often barely visible to the naked eye. Only a few millimeters in size, they are hidden in lampshades, sockets, garbage cans, alarm clocks, water bottles and toilet lids. With such, not particularly expensive monitoring devices, not only a detective brought down the then FPÖ boss Heinz-Christian Strache. Time and again, vacationers report that they accidentally come across cameras in hotel rooms and holiday apartments that voyeurs have installed on shelves and smoke alarms.
South Korea in particular has a problem with such secret recordings.
Two years ago the police arrested two men there who had filmed 1,600 hotel guests for months.
Researchers from South Korea - where the crime is known as "Molka" - and Singapore have now developed the prototype of an app that smartphone users can use to protect themselves from such spying attacks.
The IT experts call their software LAPD, which is a play on words because this abbreviation also refers to the Los Angeles Police Department.
In connection with the researcher's app, which runs on standard Android smartphones, the abbreviation means Laser Assisted Photography Detection.
The scientists gave 379 test persons a smartphone with their scanner app and had them search for previously hidden cameras.
While the test participants only discovered just under half of the cameras (46 percent) with the naked eye, which were hidden in plastic bottles, among other things, the app revealed almost twice as many lenses (88.9 percent).
The technology is in many current smartphones
It feels like "a never-ending stream of reports about people being filmed by hidden cameras," said security researcher Sriram Sami to SPIEGEL when he came up with the idea of developing such an app. So far, there has been no easy way to defend against clandestine video surveillance. "You can buy special detectors that are supposed to track down hidden cameras, but they definitely won't solve the problem."
Such detectors try to detect radio signals or magnetic fields emitted by spy cameras. In this way, according to the researchers' criticism, it is possible to prove the presence of a hidden camera. Their location, however, remains unknown. Red light sensors, which are supposed to force reflections on hidden lenses, are not as efficient as the LAPD app.
It was important to the researchers that their software works on ordinary smartphones. The only requirement: the device must be equipped with a so-called time-of-flight sensor (ToF). Such ToF chips can be found in the LG V60, the Huawei P30 and the Samsung Galaxy S20 +, for example. The Pro models of the Apple iPhones 12 and 13 with the lidar scanners also bring this technology with them. But according to the researchers, the Android devices deliver more reliable data than the interface of Apple smartphones.
The ToF sensors in smartphones are primarily used to support their cameras.
Using infrared light, they check how far away people, furniture and walls are.
The longer it takes for the light to reflect off a surface and return to the sensor, the further away the object is.
So-called augmented reality, in which computer-generated objects are built into the image of the real environment, also benefit from this technology.
With furnishing apps, for example, a virtual chair can be placed more quickly because the smartphone knows how far away the floor is.
Their size can camouflage cameras
The researchers use the scanners to look for particularly bright reflections in the room. The trick: camera lenses reflect light more strongly than most other surfaces. It's the same effect that makes cat eyes light up in the spotlight. When the infrared light from the ToF sensor hits the highly reflective lens of a mini camera, it appears on the camera image as a dark spot, which the software interprets as a hidden camera.
However, the researchers faced a problem with the many luminous dots on shiny surfaces such as aluminum foil and plastic bags. So that the app does not confuse the many reflections with spy cameras, the software first tests whether the light points are round enough. Linear and rectangular reflections are ignored. Finally, an artificial intelligence (AI) trained with 10,000 photos of miniature lenses checks whether it is a camera or perhaps just a drill hole in the wall.
However, the anti-spy camera app has a problem when the hidden cameras are unusually large.
Because the software has a filter function that sorts out round objects with a diameter of more than two millimeters.
"If an attacker manages to hide a fairly large camera, it will likely be ignored by our system," says security expert Sami.
According to "The Register", the researchers are still discussing whether they should publish the source code of their app as open source.
That would mean that developers could build on the researchers' findings.
This means that nothing stands in the way of a LAPD app that is available to everyone in the Google Play Store.
According to Sriram Sami, there are "no fundamental problems that cannot be solved with a little effort in development."