 again-without distortion of the original or loss of any information. Called "reversible data hiding," the new technique aims to solve a dilemma faced by digital image users, particularly in sensitive military, legal, and medical appli- cations. Until now they have had to choose between an image that's been watermarked to establish its trustworthiness and one that isn't watermarked but preserves all the original information, allowing it to be enlarged or enhanced to show detail. When information is embedded with this newly discovered method, authorized users can do both. "Commonly used techniques for embedding messages such as digital water- marking irreversibly change the image, resulting in distortions or information loss. While these distortions are often imperceptible or tolerable in normal applications, if the image is enlarged, enhanced, or processed using a computer, the information loss can be unacceptable," says Gaurav Sharma, an imaging QUANTUM CRYTOGRAPHY scientist at Xerox's Solutions and Services Technology Center in Webster, New York. "With our new data embedding algorithm, authorized recipients not only can extract the embedded message but also can recover the original image intact, identical bit for bit to the image before the data was added," he says. "The technique offers a significantly higher capacity for embedding data and/or a lower-distortion than any of the alternatives." "The technique will be widely applicable to situations requiring authenti- cation of images with detection of changes, and it can also be used to encode information about the image itself, such as who took the picture, when or with what camera," adds Murat Tekalp, professor of electrical engineering at the University of Rochester. "The greatest benefit of this technology is in deter- mining if anyone has clandestinely altered an image. These days many com- mercial software systems can be used to manipulate digital images. By encoding data in this way, we can be sure the image has not been tampered with, and then remove th