The Concealogram algorithm, created by Joseph Rosen, an associate professor whose interests are image processing, optics and holography, is "hard-copy" steganography, he says.

"This is not digital steganography because the secret information is not hidden inside a digital file (such as MP3s or JPEGs), but in a hard copy print, after the data leaves the computer," Rosen said. "Also, it is not chemical steganography because the secret information is neither hidden in the material of the paper nor in the ink. The secret data is encrypted within the printed visible image in a special but simple way."

The 2-D barcode is a cousin to the ubiquitous striped one-dimensional barcode. Linear barcodes hold a dozen characters that provide a reference number. The 2-D barcode, made up of a binary system of dots instead of lines, has all the information stored within so there's no need to connect to a database.

A halftone image, a common way of creating pictures, is also made up of a binary set of dots. This makes a perfect match, with one able to be slipped inside the other.

However, Concealogram does something more. Like a hologram, which stores the whole image in each part of itself, each section of the newly created "image-barcode" contains all the information that the barcode held on its own, avoiding problems caused by partial covering of the image or damage. So a scanner can pick up the person's name, social security number and fingerprint, say, even if half the picture is smudged.

"In principle, it is a very good idea," says Steve Blackmore, managing director of Datastrip, a company in the U.K. that does business in 2-D barcodes. They are not new: Datastrip has been honing its barcode-creation techniques for 12 years to increase the data storage capacity.

The company's 2-D Superscript barcode can now store around 3 kilobytes of information, enough for "a color photo and a fingerprint and lots of additional information," Blackmore said.

This could even include biometric data for face recognition.

Rosen and his two colleagues are presently establishing a company and looking for strategic partners for the commercial exploitation of the technique. The final product will be the software that creates the Concealogram by hiding the barcode inside the image and then reversing the process to extract the barcode's information when scanned by an authorized user.

Rosen has another application in mind aside from security: saving space. Hiding the barcode inside the picture or logo on a cereal packet or tube of medication would save valuable centimeters of packaging, for example. However, since the technique uses 2-D rather than linear barcodes, this would entail equipping outlets with new scanners, an expensive undertaking.

Two-dimensional barcodes are not going to replace linear barcodes in supermarkets and the like, believes Blackmore. Rather, they are ideally suited to identity cards, passports and other security-related applications.