Encryption method getting the picture

Researchers have created a new way to encrypt information in a digital image and extract it later without any distortion or loss of information.

A team of scientists from Xerox and the University of Rochester said that the technique, called reversible data hiding, could be used in situations that require proof that an image has not been altered.

Its uses could range from sensitive military and medical diagnostic images to legal documents and photographs of crime scenes. The technique could also be used to encode information within the image itself for cataloging and retrieving from databases.

Concerns about the authenticity of Web-based tickets, receipts and signed contracts have hampered the development of some e-commerce applications. While digital watermarking offers protection against tampering in most situations, it can also irreversibly change the quality of an image.

Current data-embedding techniques insert additional watermarking information, which inevitably distorts an image. While the distortion is small, it is usually irreversible. The new technique builds on previous methods but modifies the lowest levels of pixel values using data-embedding algorithms. It allows authorized viewers to extract the embedded authentication message while also removing any distortions created by the embedded information, the researchers said.

Although the technique is software-based, it could be implemented in hardware or in devices in which tightly controlling the image is critical, according the researchers.

For instance, a digital camera that carries the new algorithms could be used to gather forensic evidence for use later in a courtroom. Any subsequent manipulations of the pictures could be detected, and the area where they occurred could be pinpointed.

The technique was recently described in a research paper presented at the IEEE 2002 International Conference on Image Processing in Rochester, N.Y. It was co-developed by Mehmet U. Celik and A. Murat Tekalp of the University of Rochester and Gaurav Sharma and Eli Saber of Xerox.

The University of Rochester filed a patent application on the methods developed for reversible data hiding and plans to share the rights of the invention with Xerox.