degradation of the image. Such a watermark could make it easier to identify unauthorized images that are
shared or published.
How might this technology evolve?
Further research and development
could aim to support a wider range
of lighting conditions and camera to
subject/light source distances than
those studied to date. Research could
also tackle power consumption to enable deployment in the form of bat-tery-powered tokens or even in wearable applications. Additionally, one
might study how a level of protection
can also be realized for global shutter cameras, which the current technology cannot address, and further
understand the level of protection offered against a broader range of image processing and computational
photography techniques. More generally, one may ask whether related
ideas apply to other types of sensors
that can capture sensitive information such as microphones.
Overall, this work represents a significant step toward privacy-enhanc-ing technologies that can protect
against the capture of information
and suggests that there is a richer design space waiting to be explored.
Marco Gruteser is a research scientist at Google AI,
chair of ACM SIGMOBILE, and the Peter D. Cherasia
Faculty Scholar and professor (on leave) in the
Department of Electrical and Computing Engineering at
Rutgers University, New Brunswick, NJ, USA.
Copyright held by author.
AS CAMERAS PERVADE our lives, a defining
question is how to design technologies that can protect proprietary information and respect the privacy preferences of individuals. Mobile devices
have already significantly reduced the
effort to capture and share images.
Moreover, technology trends are moving toward continuous visual sensing
where even mobile cameras remain
always active to monitor the environment and user context. What technical approaches help balance the
convenience and usefulness of such
applications against the preferences
of subjects whose likeness or property
is captured in such recordings?
Such questions are frequently addressed through fair information
principles such as disclosure and
consent that should be incorporated
into the system design. Such consent
solutions have been difficult to apply
to camera images since a subject may
be unaware of the images being captured. Short of hiding from sight or
using masks, few systems offer provisions for opting out of having images
of one’s likeness or property recorded. Some ad hoc opt-out solutions
allow subjects to have photographs
showing their likeness or property
removed from sharing services. This
places responsibility on the subject
to identify where recordings of them
or their property are shared, a process
that is becoming increasingly onerous as the number of services using
and sharing imagery multiply.
The following paper presents a new
technique to address this issue at the
point of image capture—it stops most
digital cameras from recording a use-
ful image while the scene remains vis-
ible to human eyes. How is this pos-
sible? The authors introduce a smart
high-intensity LED light that flickers
at a high rate so that it creates a strip-
ing effect that severely degrades the
image. It exploits the rolling shutter
image sensors used in a vast major-
ity of digital cameras, where each
row in the pixel array is exposed at a
slightly different time while the cam-
era exposure control remains adjust-
ed to the average brightness over the
frame period. When the illuminating
light flickers at a rate higher than the
frame capture rate, this results in sets
of rows alternatingly over- and under-
exposed and hence the striping effect.
The human eye, however, will not perceive it, provided the flicker frequency
of the LED light is high enough, since
it essentially acts as a low-pass filter.
The degradation therefore only materializes in captured images with rolling shutter cameras.
The paper also introduces two variants of this technology. First, it shows
how specific cameras can be allowed
to take uncompromised images
while the degradation remains in effect for other unauthorized cameras.
In a corporate setting, for example,
this could allow taking photos with
company devices while making it
more difficult to capture proprietary
information with personal or visitor
devices. Second, it shows how this
technology can be used to encode
a watermark in the captured image.
This can offer a weaker form of protection, particularly in areas where
lighting conditions do not support
Lighting the Way
to Visual Privacy
By Marco Gruteser
To view the accompanying paper,
Short of hiding from
sight or using masks,
few systems offer
provisions for opting
out of having images
of one’s likeness
or property recorded.