A pair of glasses dubbed a "privacy visor" has been developed to thwart hidden cameras using facial-recognition software.
The prototype spectacles have been designed by scientists at Tokyo's National Institute of Informatics.
The glasses are equipped with a near-infrared light source, which confuses the software without affecting vision.
Law enforcers, shops and social networks are increasingly using facial-recognition software.
Prof Isao Echizen said: "As a result of developments in facial recognition technology in Google images, Facebook et cetera and the popularisation of portable terminals that append photos with photographic information [geotags]... essential measures for preventing the invasion of privacy caused by photographs taken in secret and unintentional capture in camera images is now required."
The near-infrared light "appends noise to photographed images without affecting human visibility," he said.
Prof Echizen said the glasses, which connect to a pocket power supply, would be reasonably priced, but there are some simpler alternatives.
Heavy make-up or a mask will also work, as will tilting your head at a 15-degree angle, which fools the software into thinking you do not have a face, according to an online guide produced by hacktivist group Anonymous.
In September, following a review by Ireland's data protection commissioner, Facebook suspended its facial-recognition tool that suggested when users in Europe could be tagged in photographs.
In November, it emerged some shop mannequins were collecting data on shoppers using facial-recognition software.
The EyeSee mannequin logs the age, gender and race of passers-by through a camera hidden behind one eye.