Algorithm hides data inside unaltered images

Algorithm hides data inside unaltered images
ORONO, Maine — Information can be hidden inside images without altering their appearance, according to University of Maine professor Rick Eason. In a patented algorithm he developed with Eiji Kawaguchi, a professor at the Kyushu Institute of Technology, Eason shows how to embed secret data messages within the "extra" bits of a normal bit-mapped image, which can be decoded with special software.

The new 'steganography' method hides data using a software encoder that preprocesses the image. The embedded data, which can store audio data, for example, is stored in specific portions of the image that the software encoder chooses on the fly. A matching decoder, at the receiving end, finds the hidden data and separates it from the image.

"Steganography literally means 'covered writing,' because ancient Greek spies would hide messages beneath wax-covered boards. Our method is similar, because the information is hidden right there in plain sight, but can only be recovered with our software," said Eason.

Images must be transmitted electronically, because the information is hidden in the least-significant bits, which are mostly illegible when printed. "Our algorithm looks for the most complex parts of the image — where neighboring pixels are most different from one another — and adds the hidden data to the least-significant bits of those pixels," said Eason. So unlike watermarks, which embed added information in every part of an image, only the complex parts of an image harbor the added information. Because information is hidden rather than appended, image size is unchanged.

Also, the steganography algorithm decodes the embedded data without reference to the original, or to any keys or passwords. Thus the information is not inherently secure, but is nevertheless suitable for many applications not requiring strick security.

"We have thought of many applications of our technique, such as adding text or voice data to images in digital still cameras. The added data doesn't have to be appended to the image, but can be embedded right there inside it so it can't get separated from it," said Eason.

Encryption can be added to the data before it is embedded, for security apps. Also, various parameters can be tweaked, such as just how complex a portion of the image has to be before the algorithm decides to embed info inside it.

Those tweaked parameters must be known by the receiver, acting as a password. But the inherent algorithm does not require passwords or encryption.