On Tracing Screen Photos-A Moiré Pattern-based Approach

Cyber-theft of trade secrets has become a serious business threat. Digital watermarking is a popular technique to help identify the source of the file leakage, whereby a unique watermark for each insider is hidden in sensitive files. However, malicious insiders may use smartphones to photograph the secret file displayed on screens to remove the embedded hidden digital watermarks due to the optical noises introduced during photographing. To identify the leakage source despite such
screen-photo-based leakage attacks
, we leverage Moiré pattern, an optical phenomenon resulted from the optical interaction between electronic screens and cameras. As such, we present
mID
, a new watermark-like technique that can create a carefully crafted Moiré pattern on the photo when it is taken towards the screen. We design patterns that appear to be natural yet can be linked to the identity of the leaker. We implemented
mID
and evaluated it with 7 display devices and 6 smartphones from various manufacturers and models. The results demonstrate that
mID
can achieve an average bit error rate (BER) of
$0.2\%$
and can successfully identify an ID with an average accuracy of
$98\%$
, with little influence from the type of display devices, cameras, IDs, and ambient lights.