University of Toronto logo

Multimedia Lab

The Edward S. Rogers Dept. of Electrical and Computer Engineering

Privacy Protected Surveillance Using Secure Visual Object Coding

Last Update: May 8, 2009

» Video Demonstration

Related News:

» More news...

Video surveillance of both public and private spaces is expanding at an ever-increasing rate. Consequently, individuals are increasingly concerned about the invasiveness of such ubiquitous surveillance and fear that their privacy is at risk. The demands of law enforcement agencies to prevent and prosecute criminal activity, and the need for private organizations to protect against unauthorized activities on their premises are often seen to be in conflict with the privacy requirements of individuals.

The Secure Shape and Texture Set Partitioning in Hierarchical Trees (SecST-SPIHT) secure visual object coder [1] was developed to address this. The SecST-SPIHT scheme codes the shape and texture of arbitrarily-shaped visual objects in the same fashion as ST-SPIHT [2], employing a shape-adaptive discrete wavelet transform (SA-DWT) variant and a modified SPIHT algorithm offering progressive/embedded bit-rate output. The proposed scheme incorporates a novel selective encryption algorithm, utilizing a stream cipher to encrypt a small portion of the output bit-stream. The activation of the cipher is controlled by intelligent bit-classification instructions received from the coder. The scheme efficiently and effectively secures the entire shape and texture of the object and ensures that the object cannot be reconstructed without provision of the correct decryption key; no object details are revealed without providing the exact, correct decryption key. At typical output bit-rates and choice of security parameter, the encryption operation is performed on less than 5% of the output code bits; the remaining unencrypted code bits cannot be decoded due to their dependence on the correct interpretation of the encrypted portion of the code. The progressive/embedded nature of the coder allows the output bit-rate to be varied without affecting the total number of encrypted bits or reducing security.

Original surveillance frame

Object texture encrypted using SecST-SPIHT

Object texture and shape encrypted using SecST-SPIHT

The SecST-SPIHT secure coder can be employed in surveillance systems where the capture of certain visual objects may be considered privacy invasive (e.g., face and body images). The decryption key required to decrypt and decode the visual object shape and texture may be managed such that only the appropriate authorities are able to access the object data. Furthermore, the key may be tied to the subject's identity (e.g., through RFID based tokens), thus giving control of the private content to the subject. The selective encryption procedure makes the scheme suitable for real-time applications where significant processing resources are requisitely consumed for coding of the video stream and traditional "whole content" encryption may be computationally infeasible.

This work has been cited and recommended for evaluation by the Ontario Information and Privacy Commissioner in her report on the Toronto Transit Comission (TTC) video surveillance system.

» Video Demonstration

[1] K. Martin, K.N. Plataniotis, "Privacy Protected Surveillance Using Secure Visual Object Coding," IEEE Transactions on Circuits and Systems for Video Technology: Special Issue on Video Surveillance, vol. 18, no. 8, pp. 1152-1162, Aug. 2008.

[Full technical report (2008.01) version of the above paper]

[2] K. Martin, R. Lukac, K.N. Plataniotis, "SPIHT-Based Coding of the Shape and Texture of Arbitrarily Shaped Visual Objects," IEEE Transactions on Circuits and Systems for Video Technology, vol. 16, no. 10, pp. 1196-1208, Oct. 2006.