Every picture tells a story, but how do you know that a digital photo has not been manipulated to change the tale being told? A new approach to adding an encrypted watermark to digital images allows the an image to be validated against a pass key, according to research published in the International Journal of Signal and Imaging Systems Engineering.
Visible watermarks are routinely added to digital images as a form of copy protection, but their presence essentially destroys the picture, obliterating information within altered pixels in a way that cannot be reversed. Now, Dakshinamurthi Sivakumar and Govindarajan Yamuna of Annamalai University, in Tamil Nadu, India, have developed a new, reversible watermarking scheme. The system could be used initially for the authentication of military images.

Inexpensive image editing software is now available that can be used to make essentially undetectable "photo realistic" changes to almost any photograph, the team explains. In a military setting it is important to prevent unauthorized manipulation of digital images and to be able to demonstrate credibility and provenance.